Documentation

Mathlib.CategoryTheory.Limits.Shapes.Pullbacks

Pullbacks #

We define a category WalkingCospan (resp. WalkingSpan), which is the index category for the given data for a pullback (resp. pushout) diagram. Convenience methods cospan f g and span f g construct functors from the walking (co)span, hitting the given morphisms.

We define pullback f g and pushout f g as limits and colimits of such functors.

References #

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The type of objects for the diagram indexing a pullback, defined as a special case of WidePullbackShape.

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    The central point of the walking cospan.

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      The type of objects for the diagram indexing a pushout, defined as a special case of WidePushoutShape.

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        The central point of the walking span.

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          The type of arrows for the diagram indexing a pullback.

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            The identity arrows of the walking cospan.

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              The type of arrows for the diagram indexing a pushout.

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                The identity arrows of the walking span.

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                  To construct an isomorphism of cones over the walking cospan, it suffices to construct an isomorphism of the cone points and check it commutes with the legs to left and right.

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                    To construct an isomorphism of cocones over the walking span, it suffices to construct an isomorphism of the cocone points and check it commutes with the legs from left and right.

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                      cospan f g is the functor from the walking cospan hitting f and g.

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                        span f g is the functor from the walking span hitting f and g.

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                          Every diagram indexing a pullback is naturally isomorphic (actually, equal) to a cospan

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                            Every diagram indexing a pushout is naturally isomorphic (actually, equal) to a span

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                              A functor applied to a cospan is a cospan.

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                                A functor applied to a span is a span.

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                                  def CategoryTheory.Limits.cospanExt {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :

                                  Construct an isomorphism of cospans from components.

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                                    theorem CategoryTheory.Limits.cospanExt_app_left {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                    theorem CategoryTheory.Limits.cospanExt_app_right {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                    theorem CategoryTheory.Limits.cospanExt_app_one {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                    theorem CategoryTheory.Limits.cospanExt_hom_app_left {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                    theorem CategoryTheory.Limits.cospanExt_hom_app_right {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                    theorem CategoryTheory.Limits.cospanExt_hom_app_one {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                    theorem CategoryTheory.Limits.cospanExt_inv_app_left {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                    theorem CategoryTheory.Limits.cospanExt_inv_app_right {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                    theorem CategoryTheory.Limits.cospanExt_inv_app_one {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Z} {g : Y Z} {f' : X' Z'} {g' : Y' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iZ.hom) (wg : CategoryTheory.CategoryStruct.comp iY.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
                                    def CategoryTheory.Limits.spanExt {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :

                                    Construct an isomorphism of spans from components.

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                                      theorem CategoryTheory.Limits.spanExt_app_left {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      theorem CategoryTheory.Limits.spanExt_app_right {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      theorem CategoryTheory.Limits.spanExt_app_one {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      theorem CategoryTheory.Limits.spanExt_hom_app_left {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      theorem CategoryTheory.Limits.spanExt_hom_app_right {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      theorem CategoryTheory.Limits.spanExt_hom_app_zero {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      theorem CategoryTheory.Limits.spanExt_inv_app_left {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      theorem CategoryTheory.Limits.spanExt_inv_app_right {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      theorem CategoryTheory.Limits.spanExt_inv_app_zero {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {X' : C} {Y' : C} {Z' : C} (iX : X X') (iY : Y Y') (iZ : Z Z') {f : X Y} {g : X Z} {f' : X' Y'} {g' : X' Z'} (wf : CategoryTheory.CategoryStruct.comp iX.hom f' = CategoryTheory.CategoryStruct.comp f iY.hom) (wg : CategoryTheory.CategoryStruct.comp iX.hom g' = CategoryTheory.CategoryStruct.comp g iZ.hom) :
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                                      abbrev CategoryTheory.Limits.PullbackCone {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) :
                                      Type (max u v)

                                      A pullback cone is just a cone on the cospan formed by two morphisms f : X ⟶ Z and g : Y ⟶ Z.

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                                        abbrev CategoryTheory.Limits.PullbackCone.fst {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} (t : CategoryTheory.Limits.PullbackCone f g) :
                                        t.pt X

                                        The first projection of a pullback cone.

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                                          abbrev CategoryTheory.Limits.PullbackCone.snd {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} (t : CategoryTheory.Limits.PullbackCone f g) :
                                          t.pt Y

                                          The second projection of a pullback cone.

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                                            This is a slightly more convenient method to verify that a pullback cone is a limit cone. It only asks for a proof of facts that carry any mathematical content

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                                              This is another convenient method to verify that a pullback cone is a limit cone. It only asks for a proof of facts that carry any mathematical content, and allows access to the same s for all parts.

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                                                theorem CategoryTheory.Limits.PullbackCone.mk_pt {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} {W : C} (fst : W X) (snd : W Y) (eq : CategoryTheory.CategoryStruct.comp fst f = CategoryTheory.CategoryStruct.comp snd g) :
                                                def CategoryTheory.Limits.PullbackCone.mk {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} {W : C} (fst : W X) (snd : W Y) (eq : CategoryTheory.CategoryStruct.comp fst f = CategoryTheory.CategoryStruct.comp snd g) :

                                                A pullback cone on f and g is determined by morphisms fst : W ⟶ X and snd : W ⟶ Y such that fst ≫ f = snd ≫ g.

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                                                  To construct an isomorphism of pullback cones, it suffices to construct an isomorphism of the cone points and check it commutes with fst and snd.

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                                                    If t is a limit pullback cone over f and g and h : W ⟶ X and k : W ⟶ Y are such that h ≫ f = k ≫ g, then we get l : W ⟶ t.pt, which satisfies l ≫ fst t = h and l ≫ snd t = k, see IsLimit.lift_fst and IsLimit.lift_snd.

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                                                      If t is a limit pullback cone over f and g and h : W ⟶ X and k : W ⟶ Y are such that h ≫ f = k ≫ g, then we have l : W ⟶ t.pt satisfying l ≫ fst t = h and l ≫ snd t = k.

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                                                        This is a more convenient formulation to show that a PullbackCone constructed using PullbackCone.mk is a limit cone.

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                                                          The flip of a pullback square is a pullback square.

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                                                            The pullback cone (𝟙 X, 𝟙 X) for the pair (f, f) is a limit if f is a mono. The converse is shown in mono_of_pullback_is_id.

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                                                              Suppose f and g are two morphisms with a common codomain and s is a limit cone over the diagram formed by f and g. Suppose f and g both factor through a monomorphism h via x and y, respectively. Then s is also a limit cone over the diagram formed by x and y.

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                                                                abbrev CategoryTheory.Limits.PushoutCocone {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) :
                                                                Type (max u v)

                                                                A pushout cocone is just a cocone on the span formed by two morphisms f : X ⟶ Y and g : X ⟶ Z.

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                                                                  abbrev CategoryTheory.Limits.PushoutCocone.inl {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} (t : CategoryTheory.Limits.PushoutCocone f g) :
                                                                  Y t.pt

                                                                  The first inclusion of a pushout cocone.

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                                                                    abbrev CategoryTheory.Limits.PushoutCocone.inr {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} (t : CategoryTheory.Limits.PushoutCocone f g) :
                                                                    Z t.pt

                                                                    The second inclusion of a pushout cocone.

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                                                                      This is a slightly more convenient method to verify that a pushout cocone is a colimit cocone. It only asks for a proof of facts that carry any mathematical content

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                                                                        This is another convenient method to verify that a pushout cocone is a colimit cocone. It only asks for a proof of facts that carry any mathematical content, and allows access to the same s for all parts.

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                                                                          theorem CategoryTheory.Limits.PushoutCocone.mk_pt {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} {W : C} (inl : Y W) (inr : Z W) (eq : CategoryTheory.CategoryStruct.comp f inl = CategoryTheory.CategoryStruct.comp g inr) :
                                                                          def CategoryTheory.Limits.PushoutCocone.mk {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} {W : C} (inl : Y W) (inr : Z W) (eq : CategoryTheory.CategoryStruct.comp f inl = CategoryTheory.CategoryStruct.comp g inr) :

                                                                          A pushout cocone on f and g is determined by morphisms inl : Y ⟶ W and inr : Z ⟶ W such that f ≫ inl = g ↠ inr.

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                                                                            If t is a colimit pushout cocone over f and g and h : Y ⟶ W and k : Z ⟶ W are morphisms satisfying f ≫ h = g ≫ k, then we have a factorization l : t.pt ⟶ W such that inl t ≫ l = h and inr t ≫ l = k, see IsColimit.inl_desc and IsColimit.inr_desc

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                                                                              If t is a colimit pushout cocone over f and g and h : Y ⟶ W and k : Z ⟶ W are morphisms satisfying f ≫ h = g ≫ k, then we have a factorization l : t.pt ⟶ W such that inl t ≫ l = h and inr t ≫ l = k.

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                                                                                To construct an isomorphism of pushout cocones, it suffices to construct an isomorphism of the cocone points and check it commutes with inl and inr.

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                                                                                  This is a more convenient formulation to show that a PushoutCocone constructed using PushoutCocone.mk is a colimit cocone.

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                                                                                    The flip of a pushout square is a pushout square.

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                                                                                      The pushout cocone (𝟙 X, 𝟙 X) for the pair (f, f) is a colimit if f is an epi. The converse is shown in epi_of_isColimit_mk_id_id.

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                                                                                        Suppose f and g are two morphisms with a common domain and s is a colimit cocone over the diagram formed by f and g. Suppose f and g both factor through an epimorphism h via x and y, respectively. Then s is also a colimit cocone over the diagram formed by x and y.

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                                                                                          This is a helper construction that can be useful when verifying that a category has all pullbacks. Given F : WalkingCospan ⥤ C, which is really the same as cospan (F.map inl) (F.map inr), and a pullback cone on F.map inl and F.map inr, we get a cone on F.

                                                                                          If you're thinking about using this, have a look at hasPullbacks_of_hasLimit_cospan, which you may find to be an easier way of achieving your goal.

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                                                                                            This is a helper construction that can be useful when verifying that a category has all pushout. Given F : WalkingSpan ⥤ C, which is really the same as span (F.map fst) (F.map snd), and a pushout cocone on F.map fst and F.map snd, we get a cocone on F.

                                                                                            If you're thinking about using this, have a look at hasPushouts_of_hasColimit_span, which you may find to be an easier way of achieving your goal.

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                                                                                              abbrev CategoryTheory.Limits.HasPullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) :

                                                                                              HasPullback f g represents a particular choice of limiting cone for the pair of morphisms f : X ⟶ Z and g : Y ⟶ Z.

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                                                                                                abbrev CategoryTheory.Limits.HasPushout {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) :

                                                                                                HasPushout f g represents a particular choice of colimiting cocone for the pair of morphisms f : X ⟶ Y and g : X ⟶ Z.

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                                                                                                  abbrev CategoryTheory.Limits.pullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] :
                                                                                                  C

                                                                                                  pullback f g computes the pullback of a pair of morphisms with the same target.

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                                                                                                    abbrev CategoryTheory.Limits.pushout {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) [CategoryTheory.Limits.HasPushout f g] :
                                                                                                    C

                                                                                                    pushout f g computes the pushout of a pair of morphisms with the same source.

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                                                                                                      The first projection of the pullback of f and g.

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                                                                                                        The second projection of the pullback of f and g.

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                                                                                                          The first inclusion into the pushout of f and g.

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                                                                                                            The second inclusion into the pushout of f and g.

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                                                                                                              A pair of morphisms h : W ⟶ X and k : W ⟶ Y satisfying h ≫ f = k ≫ g induces a morphism pullback.lift : W ⟶ pullback f g.

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                                                                                                                A pair of morphisms h : Y ⟶ W and k : Z ⟶ W satisfying f ≫ h = g ≫ k induces a morphism pushout.desc : pushout f g ⟶ W.

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                                                                                                                  def CategoryTheory.Limits.pullback.lift' {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} [CategoryTheory.Limits.HasPullback f g] (h : W X) (k : W Y) (w : CategoryTheory.CategoryStruct.comp h f = CategoryTheory.CategoryStruct.comp k g) :
                                                                                                                  { l // CategoryTheory.CategoryStruct.comp l CategoryTheory.Limits.pullback.fst = h CategoryTheory.CategoryStruct.comp l CategoryTheory.Limits.pullback.snd = k }

                                                                                                                  A pair of morphisms h : W ⟶ X and k : W ⟶ Y satisfying h ≫ f = k ≫ g induces a morphism l : W ⟶ pullback f g such that l ≫ pullback.fst = h and l ≫ pullback.snd = k.

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                                                                                                                    def CategoryTheory.Limits.pullback.desc' {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} [CategoryTheory.Limits.HasPushout f g] (h : Y W) (k : Z W) (w : CategoryTheory.CategoryStruct.comp f h = CategoryTheory.CategoryStruct.comp g k) :
                                                                                                                    { l // CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl l = h CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr l = k }

                                                                                                                    A pair of morphisms h : Y ⟶ W and k : Z ⟶ W satisfying f ≫ h = g ≫ k induces a morphism l : pushout f g ⟶ W such that pushout.inl ≫ l = h and pushout.inr ≫ l = k.

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                                                                                                                      theorem CategoryTheory.Limits.pullback.condition_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} [CategoryTheory.Limits.HasPullback f g] {Z : C} (h : Z Z) :
                                                                                                                      theorem CategoryTheory.Limits.pullback.condition {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} [CategoryTheory.Limits.HasPullback f g] :
                                                                                                                      CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd g
                                                                                                                      theorem CategoryTheory.Limits.pushout.condition {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} [CategoryTheory.Limits.HasPushout f g] :
                                                                                                                      CategoryTheory.CategoryStruct.comp f CategoryTheory.Limits.pushout.inl = CategoryTheory.CategoryStruct.comp g CategoryTheory.Limits.pushout.inr
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                                                                                                                      abbrev CategoryTheory.Limits.pullback.map {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} {S : C} {T : C} (f₁ : W S) (f₂ : X S) [CategoryTheory.Limits.HasPullback f₁ f₂] (g₁ : Y T) (g₂ : Z T) [CategoryTheory.Limits.HasPullback g₁ g₂] (i₁ : W Y) (i₂ : X Z) (i₃ : S T) (eq₁ : CategoryTheory.CategoryStruct.comp f₁ i₃ = CategoryTheory.CategoryStruct.comp i₁ g₁) (eq₂ : CategoryTheory.CategoryStruct.comp f₂ i₃ = CategoryTheory.CategoryStruct.comp i₂ g₂) :

                                                                                                                      Given such a diagram, then there is a natural morphism W ×ₛ X ⟶ Y ×ₜ Z.

                                                                                                                      W ⟶ Y ↘ ↘ S ⟶ T ↗ ↗ X ⟶ Z

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                                                                                                                        The canonical map X ×ₛ Y ⟶ X ×ₜ Y given S ⟶ T.

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                                                                                                                          abbrev CategoryTheory.Limits.pushout.map {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} {S : C} {T : C} (f₁ : S W) (f₂ : S X) [CategoryTheory.Limits.HasPushout f₁ f₂] (g₁ : T Y) (g₂ : T Z) [CategoryTheory.Limits.HasPushout g₁ g₂] (i₁ : W Y) (i₂ : X Z) (i₃ : S T) (eq₁ : CategoryTheory.CategoryStruct.comp f₁ i₁ = CategoryTheory.CategoryStruct.comp i₃ g₁) (eq₂ : CategoryTheory.CategoryStruct.comp f₂ i₂ = CategoryTheory.CategoryStruct.comp i₃ g₂) :

                                                                                                                          Given such a diagram, then there is a natural morphism W ⨿ₛ X ⟶ Y ⨿ₜ Z.

                                                                                                                          W ⟶ Y
                                                                                                                          

                                                                                                                          ↗ ↗ S ⟶ T ↘ ↘ X ⟶ Z

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                                                                                                                            The canonical map X ⨿ₛ Y ⟶ X ⨿ₜ Y given S ⟶ T.

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                                                                                                                              theorem CategoryTheory.Limits.pullback.hom_ext {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} [CategoryTheory.Limits.HasPullback f g] {W : C} {k : W CategoryTheory.Limits.pullback f g} {l : W CategoryTheory.Limits.pullback f g} (h₀ : CategoryTheory.CategoryStruct.comp k CategoryTheory.Limits.pullback.fst = CategoryTheory.CategoryStruct.comp l CategoryTheory.Limits.pullback.fst) (h₁ : CategoryTheory.CategoryStruct.comp k CategoryTheory.Limits.pullback.snd = CategoryTheory.CategoryStruct.comp l CategoryTheory.Limits.pullback.snd) :
                                                                                                                              k = l

                                                                                                                              Two morphisms into a pullback are equal if their compositions with the pullback morphisms are equal

                                                                                                                              def CategoryTheory.Limits.pullbackIsPullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] :
                                                                                                                              CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd g))

                                                                                                                              The pullback cone built from the pullback projections is a pullback.

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                                                                                                                                instance CategoryTheory.Limits.pullback.fst_of_mono {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Mono g] :
                                                                                                                                CategoryTheory.Mono CategoryTheory.Limits.pullback.fst

                                                                                                                                The pullback of a monomorphism is a monomorphism

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                                                                                                                                instance CategoryTheory.Limits.pullback.snd_of_mono {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Z} {g : Y Z} [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Mono f] :
                                                                                                                                CategoryTheory.Mono CategoryTheory.Limits.pullback.snd

                                                                                                                                The pullback of a monomorphism is a monomorphism

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                                                                                                                                instance CategoryTheory.Limits.mono_pullback_to_prod {C : Type u_1} [CategoryTheory.Category.{u_2, u_1} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasBinaryProduct X Y] :
                                                                                                                                CategoryTheory.Mono (CategoryTheory.Limits.prod.lift CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd)

                                                                                                                                The map X ×[Z] Y ⟶ X × Y is mono.

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                                                                                                                                theorem CategoryTheory.Limits.pushout.hom_ext {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} [CategoryTheory.Limits.HasPushout f g] {W : C} {k : CategoryTheory.Limits.pushout f g W} {l : CategoryTheory.Limits.pushout f g W} (h₀ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl k = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl l) (h₁ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr k = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr l) :
                                                                                                                                k = l

                                                                                                                                Two morphisms out of a pushout are equal if their compositions with the pushout morphisms are equal

                                                                                                                                def CategoryTheory.Limits.pushoutIsPushout {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) [CategoryTheory.Limits.HasPushout f g] :
                                                                                                                                CategoryTheory.Limits.IsColimit (CategoryTheory.Limits.PushoutCocone.mk CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr (_ : CategoryTheory.CategoryStruct.comp f CategoryTheory.Limits.pushout.inl = CategoryTheory.CategoryStruct.comp g CategoryTheory.Limits.pushout.inr))

                                                                                                                                The pushout cocone built from the pushout coprojections is a pushout.

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                                                                                                                                  instance CategoryTheory.Limits.pushout.inl_of_epi {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Epi g] :
                                                                                                                                  CategoryTheory.Epi CategoryTheory.Limits.pushout.inl

                                                                                                                                  The pushout of an epimorphism is an epimorphism

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                                                                                                                                  instance CategoryTheory.Limits.pushout.inr_of_epi {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f : X Y} {g : X Z} [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Epi f] :
                                                                                                                                  CategoryTheory.Epi CategoryTheory.Limits.pushout.inr

                                                                                                                                  The pushout of an epimorphism is an epimorphism

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                                                                                                                                  instance CategoryTheory.Limits.pullback.map_isIso {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} {S : C} {T : C} (f₁ : W S) (f₂ : X S) [CategoryTheory.Limits.HasPullback f₁ f₂] (g₁ : Y T) (g₂ : Z T) [CategoryTheory.Limits.HasPullback g₁ g₂] (i₁ : W Y) (i₂ : X Z) (i₃ : S T) (eq₁ : CategoryTheory.CategoryStruct.comp f₁ i₃ = CategoryTheory.CategoryStruct.comp i₁ g₁) (eq₂ : CategoryTheory.CategoryStruct.comp f₂ i₃ = CategoryTheory.CategoryStruct.comp i₂ g₂) [CategoryTheory.IsIso i₁] [CategoryTheory.IsIso i₂] [CategoryTheory.IsIso i₃] :
                                                                                                                                  CategoryTheory.IsIso (CategoryTheory.Limits.pullback.map f₁ f₂ g₁ g₂ i₁ i₂ i₃ eq₁ eq₂)
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                                                                                                                                  def CategoryTheory.Limits.pullback.congrHom {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f₁ : X Z} {f₂ : X Z} {g₁ : Y Z} {g₂ : Y Z} (h₁ : f₁ = f₂) (h₂ : g₁ = g₂) [CategoryTheory.Limits.HasPullback f₁ g₁] [CategoryTheory.Limits.HasPullback f₂ g₂] :

                                                                                                                                  If f₁ = f₂ and g₁ = g₂, we may construct a canonical isomorphism pullback f₁ g₁ ≅ pullback f₂ g₂

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                                                                                                                                    instance CategoryTheory.Limits.pushout.map_isIso {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} {S : C} {T : C} (f₁ : S W) (f₂ : S X) [CategoryTheory.Limits.HasPushout f₁ f₂] (g₁ : T Y) (g₂ : T Z) [CategoryTheory.Limits.HasPushout g₁ g₂] (i₁ : W Y) (i₂ : X Z) (i₃ : S T) (eq₁ : CategoryTheory.CategoryStruct.comp f₁ i₁ = CategoryTheory.CategoryStruct.comp i₃ g₁) (eq₂ : CategoryTheory.CategoryStruct.comp f₂ i₂ = CategoryTheory.CategoryStruct.comp i₃ g₂) [CategoryTheory.IsIso i₁] [CategoryTheory.IsIso i₂] [CategoryTheory.IsIso i₃] :
                                                                                                                                    CategoryTheory.IsIso (CategoryTheory.Limits.pushout.map f₁ f₂ g₁ g₂ i₁ i₂ i₃ eq₁ eq₂)
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                                                                                                                                    def CategoryTheory.Limits.pushout.congrHom {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} {f₁ : X Y} {f₂ : X Y} {g₁ : X Z} {g₂ : X Z} (h₁ : f₁ = f₂) (h₂ : g₁ = g₂) [CategoryTheory.Limits.HasPushout f₁ g₁] [CategoryTheory.Limits.HasPushout f₂ g₂] :

                                                                                                                                    If f₁ = f₂ and g₁ = g₂, we may construct a canonical isomorphism pushout f₁ g₁ ≅ pullback f₂ g₂

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                                                                                                                                      The comparison morphism for the pullback of f,g. This is an isomorphism iff G preserves the pullback of f,g; see CategoryTheory/Limits/Preserves/Shapes/Pullbacks.lean

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                                                                                                                                        theorem CategoryTheory.Limits.pullbackComparison_comp_fst_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] {X : C} {Y : C} {Z : C} (G : CategoryTheory.Functor C D) (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback (G.map f) (G.map g)] {Z : D} (h : G.obj X Z) :
                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackComparison G f g) (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst h) = CategoryTheory.CategoryStruct.comp (G.map CategoryTheory.Limits.pullback.fst) h
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                                                                                                                                        theorem CategoryTheory.Limits.pullbackComparison_comp_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] {X : C} {Y : C} {Z : C} (G : CategoryTheory.Functor C D) (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback (G.map f) (G.map g)] :
                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackComparison G f g) CategoryTheory.Limits.pullback.fst = G.map CategoryTheory.Limits.pullback.fst
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                                                                                                                                        theorem CategoryTheory.Limits.pullbackComparison_comp_snd_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] {X : C} {Y : C} {Z : C} (G : CategoryTheory.Functor C D) (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback (G.map f) (G.map g)] {Z : D} (h : G.obj Y Z) :
                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackComparison G f g) (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h) = CategoryTheory.CategoryStruct.comp (G.map CategoryTheory.Limits.pullback.snd) h
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                                                                                                                                        theorem CategoryTheory.Limits.pullbackComparison_comp_snd {C : Type u} [CategoryTheory.Category.{v, u} C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] {X : C} {Y : C} {Z : C} (G : CategoryTheory.Functor C D) (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback (G.map f) (G.map g)] :
                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackComparison G f g) CategoryTheory.Limits.pullback.snd = G.map CategoryTheory.Limits.pullback.snd

                                                                                                                                        The comparison morphism for the pushout of f,g. This is an isomorphism iff G preserves the pushout of f,g; see CategoryTheory/Limits/Preserves/Shapes/Pullbacks.lean

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                                                                                                                                          theorem CategoryTheory.Limits.inl_comp_pushoutComparison {C : Type u} [CategoryTheory.Category.{v, u} C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] {X : C} {Y : C} {Z : C} (G : CategoryTheory.Functor C D) (f : X Y) (g : X Z) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout (G.map f) (G.map g)] :
                                                                                                                                          CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutComparison G f g) = G.map CategoryTheory.Limits.pushout.inl
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                                                                                                                                          theorem CategoryTheory.Limits.inr_comp_pushoutComparison {C : Type u} [CategoryTheory.Category.{v, u} C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] {X : C} {Y : C} {Z : C} (G : CategoryTheory.Functor C D) (f : X Y) (g : X Z) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout (G.map f) (G.map g)] :
                                                                                                                                          CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushoutComparison G f g) = G.map CategoryTheory.Limits.pushout.inr

                                                                                                                                          Making this a global instance would make the typeclass search go in an infinite loop.

                                                                                                                                          The isomorphism X ×[Z] Y ≅ Y ×[Z] X.

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                                                                                                                                            theorem CategoryTheory.Limits.pullbackSymmetry_hom_comp_fst_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] {Z : C} (h : Y Z) :
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                                                                                                                                            theorem CategoryTheory.Limits.pullbackSymmetry_hom_comp_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] :
                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackSymmetry f g).hom CategoryTheory.Limits.pullback.fst = CategoryTheory.Limits.pullback.snd
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                                                                                                                                            theorem CategoryTheory.Limits.pullbackSymmetry_hom_comp_snd_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] {Z : C} (h : X Z) :
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                                                                                                                                            theorem CategoryTheory.Limits.pullbackSymmetry_hom_comp_snd {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] :
                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackSymmetry f g).hom CategoryTheory.Limits.pullback.snd = CategoryTheory.Limits.pullback.fst
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                                                                                                                                            theorem CategoryTheory.Limits.pullbackSymmetry_inv_comp_fst_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] {Z : C} (h : X Z) :
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                                                                                                                                            theorem CategoryTheory.Limits.pullbackSymmetry_inv_comp_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] :
                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackSymmetry f g).inv CategoryTheory.Limits.pullback.fst = CategoryTheory.Limits.pullback.snd
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                                                                                                                                            theorem CategoryTheory.Limits.pullbackSymmetry_inv_comp_snd_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] {Z : C} (h : Y Z) :
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                                                                                                                                            theorem CategoryTheory.Limits.pullbackSymmetry_inv_comp_snd {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) [CategoryTheory.Limits.HasPullback f g] :
                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackSymmetry f g).inv CategoryTheory.Limits.pullback.snd = CategoryTheory.Limits.pullback.fst

                                                                                                                                            Making this a global instance would make the typeclass search go in an infinite loop.

                                                                                                                                            The isomorphism Y ⨿[X] Z ≅ Z ⨿[X] Y.

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                                                                                                                                              theorem CategoryTheory.Limits.inl_comp_pushoutSymmetry_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) [CategoryTheory.Limits.HasPushout f g] :
                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutSymmetry f g).hom = CategoryTheory.Limits.pushout.inr
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                                                                                                                                              theorem CategoryTheory.Limits.inr_comp_pushoutSymmetry_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) [CategoryTheory.Limits.HasPushout f g] :
                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushoutSymmetry f g).hom = CategoryTheory.Limits.pushout.inl
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                                                                                                                                              theorem CategoryTheory.Limits.inl_comp_pushoutSymmetry_inv {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) [CategoryTheory.Limits.HasPushout f g] :
                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutSymmetry f g).inv = CategoryTheory.Limits.pushout.inr
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                                                                                                                                              theorem CategoryTheory.Limits.inr_comp_pushoutSymmetry_inv {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) [CategoryTheory.Limits.HasPushout f g] :
                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushoutSymmetry f g).inv = CategoryTheory.Limits.pushout.inl
                                                                                                                                              noncomputable def CategoryTheory.Limits.pullbackIsPullbackOfCompMono {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X W) (g : Y W) (i : W Z) [CategoryTheory.Mono i] [CategoryTheory.Limits.HasPullback f g] :
                                                                                                                                              CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp f i) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd (CategoryTheory.CategoryStruct.comp g i)))

                                                                                                                                              The pullback of f, g is also the pullback of f ≫ i, g ≫ i for any mono i.

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                                                                                                                                                If f : X ⟶ Z is iso, then X ×[Z] Y ≅ Y. This is the explicit limit cone.

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                                                                                                                                                  Verify that the constructed limit cone is indeed a limit.

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                                                                                                                                                    If g : Y ⟶ Z is iso, then X ×[Z] Y ≅ X. This is the explicit limit cone.

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                                                                                                                                                      Verify that the constructed limit cone is indeed a limit.

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                                                                                                                                                        noncomputable def CategoryTheory.Limits.pushoutIsPushoutOfEpiComp {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) (h : W X) [CategoryTheory.Epi h] [CategoryTheory.Limits.HasPushout f g] :
                                                                                                                                                        CategoryTheory.Limits.IsColimit (CategoryTheory.Limits.PushoutCocone.mk CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp h f) CategoryTheory.Limits.pushout.inl = CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp h g) CategoryTheory.Limits.pushout.inr))

                                                                                                                                                        The pushout of f, g is also the pullback of h ≫ f, h ≫ g for any epi h.

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                                                                                                                                                          If f : X ⟶ Y is iso, then Y ⨿[X] Z ≅ Z. This is the explicit colimit cocone.

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                                                                                                                                                            Verify that the constructed cocone is indeed a colimit.

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                                                                                                                                                              If f : X ⟶ Z is iso, then Y ⨿[X] Z ≅ Y. This is the explicit colimit cocone.

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                                                                                                                                                                Verify that the constructed cocone is indeed a colimit.

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                                                                                                                                                                  theorem CategoryTheory.Limits.fst_eq_snd_of_mono_eq {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} (f : X Y) [CategoryTheory.Mono f] :
                                                                                                                                                                  CategoryTheory.Limits.pullback.fst = CategoryTheory.Limits.pullback.snd
                                                                                                                                                                  theorem CategoryTheory.Limits.inl_eq_inr_of_epi_eq {C : Type u} [CategoryTheory.Category.{v, u} C] {X : C} {Y : C} (f : X Y) [CategoryTheory.Epi f] :
                                                                                                                                                                  CategoryTheory.Limits.pushout.inl = CategoryTheory.Limits.pushout.inr
                                                                                                                                                                  def CategoryTheory.Limits.bigSquareIsPullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} {Y₃ : C} (f₁ : X₁ X₂) (f₂ : X₂ X₃) (g₁ : Y₁ Y₂) (g₂ : Y₂ Y₃) (i₁ : X₁ Y₁) (i₂ : X₂ Y₂) (i₃ : X₃ Y₃) (h₁ : CategoryTheory.CategoryStruct.comp i₁ g₁ = CategoryTheory.CategoryStruct.comp f₁ i₂) (h₂ : CategoryTheory.CategoryStruct.comp i₂ g₂ = CategoryTheory.CategoryStruct.comp f₂ i₃) (H : CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk i₂ f₂ h₂)) (H' : CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk i₁ f₁ h₁)) :

                                                                                                                                                                  Given

                                                                                                                                                                  X₁ - f₁ -> X₂ - f₂ -> X₃ | | | i₁ i₂ i₃ ∨ ∨ ∨ Y₁ - g₁ -> Y₂ - g₂ -> Y₃

                                                                                                                                                                  Then the big square is a pullback if both the small squares are.

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                                                                                                                                                                    Given

                                                                                                                                                                    X₁ - f₁ -> X₂ - f₂ -> X₃ | | | i₁ i₂ i₃ ∨ ∨ ∨ Y₁ - g₁ -> Y₂ - g₂ -> Y₃

                                                                                                                                                                    Then the big square is a pushout if both the small squares are.

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                                                                                                                                                                      def CategoryTheory.Limits.leftSquareIsPullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} {Y₃ : C} (f₁ : X₁ X₂) (f₂ : X₂ X₃) (g₁ : Y₁ Y₂) (g₂ : Y₂ Y₃) (i₁ : X₁ Y₁) (i₂ : X₂ Y₂) (i₃ : X₃ Y₃) (h₁ : CategoryTheory.CategoryStruct.comp i₁ g₁ = CategoryTheory.CategoryStruct.comp f₁ i₂) (h₂ : CategoryTheory.CategoryStruct.comp i₂ g₂ = CategoryTheory.CategoryStruct.comp f₂ i₃) (H : CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk i₂ f₂ h₂)) (H' : CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk i₁ (CategoryTheory.CategoryStruct.comp f₁ f₂) (_ : CategoryTheory.CategoryStruct.comp i₁ (CategoryTheory.CategoryStruct.comp g₁ g₂) = CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp f₁ f₂) i₃))) :

                                                                                                                                                                      Given

                                                                                                                                                                      X₁ - f₁ -> X₂ - f₂ -> X₃ | | | i₁ i₂ i₃ ∨ ∨ ∨ Y₁ - g₁ -> Y₂ - g₂ -> Y₃

                                                                                                                                                                      Then the left square is a pullback if the right square and the big square are.

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                                                                                                                                                                        Given

                                                                                                                                                                        X₁ - f₁ -> X₂ - f₂ -> X₃ | | | i₁ i₂ i₃ ∨ ∨ ∨ Y₁ - g₁ -> Y₂ - g₂ -> Y₃

                                                                                                                                                                        Then the right square is a pushout if the left square and the big square are.

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                                                                                                                                                                          The canonical isomorphism W ×[X] (X ×[Z] Y) ≅ W ×[Z] Y

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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_hom_fst_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] {Z : C} (h : W Z) :
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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_hom_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] :
                                                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackRightPullbackFstIso f g f').hom CategoryTheory.Limits.pullback.fst = CategoryTheory.Limits.pullback.fst
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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_hom_snd_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] {Z : C} (h : Y Z) :
                                                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackRightPullbackFstIso f g f').hom (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h)
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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_hom_snd {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] :
                                                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackRightPullbackFstIso f g f').hom CategoryTheory.Limits.pullback.snd = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.snd
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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_inv_fst_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] {Z : C} (h : W Z) :
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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_inv_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] :
                                                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackRightPullbackFstIso f g f').inv CategoryTheory.Limits.pullback.fst = CategoryTheory.Limits.pullback.fst
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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_inv_snd_snd_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] {Z : C} (h : Y Z) :
                                                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackRightPullbackFstIso f g f').inv (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h
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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_inv_snd_snd {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] :
                                                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackRightPullbackFstIso f g f').inv (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.snd) = CategoryTheory.Limits.pullback.snd
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                                                                                                                                                                            theorem CategoryTheory.Limits.pullbackRightPullbackFstIso_inv_snd_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Z) (g : Y Z) (f' : W X) [CategoryTheory.Limits.HasPullback f g] [CategoryTheory.Limits.HasPullback f' CategoryTheory.Limits.pullback.fst] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp f' f) g] :
                                                                                                                                                                            CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackRightPullbackFstIso f g f').inv (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f'

                                                                                                                                                                            The canonical isomorphism (Y ⨿[X] Z) ⨿[Z] W ≅ Y ×[X] W

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                                                                                                                                                                              theorem CategoryTheory.Limits.inl_pushoutLeftPushoutInrIso_inv_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) (g' : Z W) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout CategoryTheory.Limits.pushout.inr g'] [CategoryTheory.Limits.HasPushout f (CategoryTheory.CategoryStruct.comp g g')] {Z : C} (h : CategoryTheory.Limits.pushout CategoryTheory.Limits.pushout.inr g' Z) :
                                                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pushoutLeftPushoutInrIso f g g').inv h) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl h)
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                                                                                                                                                                              theorem CategoryTheory.Limits.inl_pushoutLeftPushoutInrIso_inv {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) (g' : Z W) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout CategoryTheory.Limits.pushout.inr g'] [CategoryTheory.Limits.HasPushout f (CategoryTheory.CategoryStruct.comp g g')] :
                                                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutLeftPushoutInrIso f g g').inv = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inl
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                                                                                                                                                                              theorem CategoryTheory.Limits.inr_pushoutLeftPushoutInrIso_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) (g' : Z W) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout CategoryTheory.Limits.pushout.inr g'] [CategoryTheory.Limits.HasPushout f (CategoryTheory.CategoryStruct.comp g g')] :
                                                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushoutLeftPushoutInrIso f g g').hom = CategoryTheory.Limits.pushout.inr
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                                                                                                                                                                              theorem CategoryTheory.Limits.inr_pushoutLeftPushoutInrIso_inv_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) (g' : Z W) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout CategoryTheory.Limits.pushout.inr g'] [CategoryTheory.Limits.HasPushout f (CategoryTheory.CategoryStruct.comp g g')] {Z : C} (h : CategoryTheory.Limits.pushout CategoryTheory.Limits.pushout.inr g' Z) :
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                                                                                                                                                                              theorem CategoryTheory.Limits.inr_pushoutLeftPushoutInrIso_inv {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) (g' : Z W) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout CategoryTheory.Limits.pushout.inr g'] [CategoryTheory.Limits.HasPushout f (CategoryTheory.CategoryStruct.comp g g')] :
                                                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushoutLeftPushoutInrIso f g g').inv = CategoryTheory.Limits.pushout.inr
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                                                                                                                                                                              theorem CategoryTheory.Limits.inl_inl_pushoutLeftPushoutInrIso_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) (g' : Z W) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout CategoryTheory.Limits.pushout.inr g'] [CategoryTheory.Limits.HasPushout f (CategoryTheory.CategoryStruct.comp g g')] :
                                                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutLeftPushoutInrIso f g g').hom) = CategoryTheory.Limits.pushout.inl
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                                                                                                                                                                              theorem CategoryTheory.Limits.inr_inl_pushoutLeftPushoutInrIso_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {W : C} {X : C} {Y : C} {Z : C} (f : X Y) (g : X Z) (g' : Z W) [CategoryTheory.Limits.HasPushout f g] [CategoryTheory.Limits.HasPushout CategoryTheory.Limits.pushout.inr g'] [CategoryTheory.Limits.HasPushout f (CategoryTheory.CategoryStruct.comp g g')] :
                                                                                                                                                                              CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutLeftPushoutInrIso f g g').hom) = CategoryTheory.CategoryStruct.comp g' CategoryTheory.Limits.pushout.inr
                                                                                                                                                                              def CategoryTheory.Limits.pullbackPullbackLeftIsPullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] :
                                                                                                                                                                              CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk CategoryTheory.Limits.pullback.fst (CategoryTheory.Limits.pullback.lift (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) CategoryTheory.Limits.pullback.snd (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) f₃ = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₄)) (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd = CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullback.lift (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) CategoryTheory.Limits.pullback.snd (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) f₃ = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₄)) CategoryTheory.Limits.pullback.fst))

                                                                                                                                                                              (X₁ ×[Y₁] X₂) ×[Y₂] X₃ is the pullback (X₁ ×[Y₁] X₂) ×[X₂] (X₂ ×[Y₂] X₃).

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                                                                                                                                                                                def CategoryTheory.Limits.pullbackAssocIsPullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] :
                                                                                                                                                                                CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.fst) (CategoryTheory.Limits.pullback.lift (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) CategoryTheory.Limits.pullback.snd (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) f₃ = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₄)) (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.fst) f₁ = CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullback.lift (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) CategoryTheory.Limits.pullback.snd (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) f₃ = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₄)) (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)))

                                                                                                                                                                                (X₁ ×[Y₁] X₂) ×[Y₂] X₃ is the pullback X₁ ×[Y₁] (X₂ ×[Y₂] X₃).

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                                                                                                                                                                                  theorem CategoryTheory.Limits.hasPullback_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] :
                                                                                                                                                                                  CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)
                                                                                                                                                                                  def CategoryTheory.Limits.pullbackPullbackRightIsPullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                  CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk (CategoryTheory.Limits.pullback.lift CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₁ = CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) f₂)) CategoryTheory.Limits.pullback.snd (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullback.lift CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₁ = CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) f₂)) CategoryTheory.Limits.pullback.snd = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst))

                                                                                                                                                                                  X₁ ×[Y₁] (X₂ ×[Y₂] X₃) is the pullback (X₁ ×[Y₁] X₂) ×[X₂] (X₂ ×[Y₂] X₃).

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                                                                                                                                                                                    def CategoryTheory.Limits.pullbackAssocSymmIsPullback {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                    CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.PullbackCone.mk (CategoryTheory.Limits.pullback.lift CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₁ = CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) f₂)) (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.snd) (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullback.lift CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₁ = CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) f₂)) (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) = CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.snd) f₄))

                                                                                                                                                                                    X₁ ×[Y₁] (X₂ ×[Y₂] X₃) is the pullback (X₁ ×[Y₁] X₂) ×[Y₂] X₃.

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                                                                                                                                                                                      theorem CategoryTheory.Limits.hasPullback_assoc_symm {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                      CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄
                                                                                                                                                                                      noncomputable def CategoryTheory.Limits.pullbackAssoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                      CategoryTheory.Limits.pullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄ CategoryTheory.Limits.pullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)

                                                                                                                                                                                      The canonical isomorphism (X₁ ×[Y₁] X₂) ×[Y₂] X₃ ≅ X₁ ×[Y₁] (X₂ ×[Y₂] X₃).

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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_inv_fst_fst_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] {Z : C} (h : X₁ Z) :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).inv (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst h
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_inv_fst_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).inv (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.fst) = CategoryTheory.Limits.pullback.fst
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_hom_fst_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] {Z : C} (h : X₁ Z) :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).hom (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst h) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst h)
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_hom_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).hom CategoryTheory.Limits.pullback.fst = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.fst
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_hom_snd_fst_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] {Z : C} (h : X₂ Z) :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).hom (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h)
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_hom_snd_fst {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).hom (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_hom_snd_snd_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] {Z : C} (h : X₃ Z) :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).hom (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_hom_snd_snd {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).hom (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.snd) = CategoryTheory.Limits.pullback.snd
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_inv_fst_snd_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] {Z : C} (h : X₂ Z) :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).inv (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst h)
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_inv_fst_snd {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).inv (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst CategoryTheory.Limits.pullback.snd) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.fst
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_inv_snd_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] {Z : C} (h : X₃ Z) :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).inv (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd h)
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                                                                                                                                                                                        theorem CategoryTheory.Limits.pullbackAssoc_inv_snd {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Y₁ : C} {Y₂ : C} (f₁ : X₁ Y₁) (f₂ : X₂ Y₁) (f₃ : X₂ Y₂) (f₄ : X₃ Y₂) [CategoryTheory.Limits.HasPullback f₁ f₂] [CategoryTheory.Limits.HasPullback f₃ f₄] [CategoryTheory.Limits.HasPullback (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd f₃) f₄] [CategoryTheory.Limits.HasPullback f₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst f₂)] :
                                                                                                                                                                                        CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pullbackAssoc f₁ f₂ f₃ f₄).inv CategoryTheory.Limits.pullback.snd = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.snd CategoryTheory.Limits.pullback.snd
                                                                                                                                                                                        def CategoryTheory.Limits.pushoutPushoutLeftIsPushout {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] :
                                                                                                                                                                                        CategoryTheory.Limits.IsColimit (CategoryTheory.Limits.PushoutCocone.mk CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushout.desc (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl) CategoryTheory.Limits.pushout.inr (_ : CategoryTheory.CategoryStruct.comp g₃ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl) = CategoryTheory.CategoryStruct.comp g₄ CategoryTheory.Limits.pushout.inr)) (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushout.desc (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl) CategoryTheory.Limits.pushout.inr (_ : CategoryTheory.CategoryStruct.comp g₃ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl) = CategoryTheory.CategoryStruct.comp g₄ CategoryTheory.Limits.pushout.inr))))

                                                                                                                                                                                        (X₁ ⨿[Z₁] X₂) ⨿[Z₂] X₃ is the pushout (X₁ ⨿[Z₁] X₂) ×[X₂] (X₂ ⨿[Z₂] X₃).

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                                                                                                                                                                                          def CategoryTheory.Limits.pushoutAssocIsPushout {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] :
                                                                                                                                                                                          CategoryTheory.Limits.IsColimit (CategoryTheory.Limits.PushoutCocone.mk (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inl) (CategoryTheory.Limits.pushout.desc (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl) CategoryTheory.Limits.pushout.inr (_ : CategoryTheory.CategoryStruct.comp g₃ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl) = CategoryTheory.CategoryStruct.comp g₄ CategoryTheory.Limits.pushout.inr)) (_ : CategoryTheory.CategoryStruct.comp g₁ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inl) = CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl) (CategoryTheory.Limits.pushout.desc (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl) CategoryTheory.Limits.pushout.inr (_ : CategoryTheory.CategoryStruct.comp g₃ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl) = CategoryTheory.CategoryStruct.comp g₄ CategoryTheory.Limits.pushout.inr))))

                                                                                                                                                                                          (X₁ ⨿[Z₁] X₂) ⨿[Z₂] X₃ is the pushout X₁ ⨿[Z₁] (X₂ ⨿[Z₂] X₃).

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                                                                                                                                                                                            theorem CategoryTheory.Limits.hasPushout_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] :
                                                                                                                                                                                            CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)
                                                                                                                                                                                            def CategoryTheory.Limits.pushoutPushoutRightIsPushout {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                            CategoryTheory.Limits.IsColimit (CategoryTheory.Limits.PushoutCocone.mk (CategoryTheory.Limits.pushout.desc CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr) (_ : CategoryTheory.CategoryStruct.comp g₁ CategoryTheory.Limits.pushout.inl = CategoryTheory.CategoryStruct.comp g₂ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr))) CategoryTheory.Limits.pushout.inr (_ : CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushout.desc CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr) (_ : CategoryTheory.CategoryStruct.comp g₁ CategoryTheory.Limits.pushout.inl = CategoryTheory.CategoryStruct.comp g₂ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr))) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr))

                                                                                                                                                                                            X₁ ⨿[Z₁] (X₂ ⨿[Z₂] X₃) is the pushout (X₁ ⨿[Z₁] X₂) ×[X₂] (X₂ ⨿[Z₂] X₃).

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                                                                                                                                                                                              def CategoryTheory.Limits.pushoutAssocSymmIsPushout {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                              CategoryTheory.Limits.IsColimit (CategoryTheory.Limits.PushoutCocone.mk (CategoryTheory.Limits.pushout.desc CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr) (_ : CategoryTheory.CategoryStruct.comp g₁ CategoryTheory.Limits.pushout.inl = CategoryTheory.CategoryStruct.comp g₂ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr))) (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inr) (_ : CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) (CategoryTheory.Limits.pushout.desc CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr) (_ : CategoryTheory.CategoryStruct.comp g₁ CategoryTheory.Limits.pushout.inl = CategoryTheory.CategoryStruct.comp g₂ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr))) = CategoryTheory.CategoryStruct.comp g₄ (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inr)))

                                                                                                                                                                                              X₁ ⨿[Z₁] (X₂ ⨿[Z₂] X₃) is the pushout (X₁ ⨿[Z₁] X₂) ⨿[Z₂] X₃.

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                                                                                                                                                                                                theorem CategoryTheory.Limits.hasPushout_assoc_symm {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                                CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄
                                                                                                                                                                                                noncomputable def CategoryTheory.Limits.pushoutAssoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                                CategoryTheory.Limits.pushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄ CategoryTheory.Limits.pushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)

                                                                                                                                                                                                The canonical isomorphism (X₁ ⨿[Z₁] X₂) ⨿[Z₂] X₃ ≅ X₁ ⨿[Z₁] (X₂ ⨿[Z₂] X₃).

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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inl_inl_pushoutAssoc_hom_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] {Z : C} (h : CategoryTheory.Limits.pushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl) Z) :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).hom h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl h
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inl_inl_pushoutAssoc_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).hom) = CategoryTheory.Limits.pushout.inl
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inr_inl_pushoutAssoc_hom_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] {Z : C} (h : CategoryTheory.Limits.pushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl) Z) :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).hom h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr h)
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inr_inl_pushoutAssoc_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).hom) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inr
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inr_inr_pushoutAssoc_inv_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] {Z : C} (h : CategoryTheory.Limits.pushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄ Z) :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).inv h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr h
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inr_inr_pushoutAssoc_inv {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).inv) = CategoryTheory.Limits.pushout.inr
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inl_pushoutAssoc_inv_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] {Z : C} (h : CategoryTheory.Limits.pushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄ Z) :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).inv h) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl h)
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inl_pushoutAssoc_inv {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).inv = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl CategoryTheory.Limits.pushout.inl
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inl_inr_pushoutAssoc_inv_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] {Z : C} (h : CategoryTheory.Limits.pushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄ Z) :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).inv h)) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl h)
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inl_inr_pushoutAssoc_inv {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inl (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).inv) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inl
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inr_pushoutAssoc_hom_assoc {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] {Z : C} (h : CategoryTheory.Limits.pushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl) Z) :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).hom h) = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr h)
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                                                                                                                                                                                                  theorem CategoryTheory.Limits.inr_pushoutAssoc_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {X₁ : C} {X₂ : C} {X₃ : C} {Z₁ : C} {Z₂ : C} (g₁ : Z₁ X₁) (g₂ : Z₁ X₂) (g₃ : Z₂ X₂) (g₄ : Z₂ X₃) [CategoryTheory.Limits.HasPushout g₁ g₂] [CategoryTheory.Limits.HasPushout g₃ g₄] [CategoryTheory.Limits.HasPushout (CategoryTheory.CategoryStruct.comp g₃ CategoryTheory.Limits.pushout.inr) g₄] [CategoryTheory.Limits.HasPushout g₁ (CategoryTheory.CategoryStruct.comp g₂ CategoryTheory.Limits.pushout.inl)] :
                                                                                                                                                                                                  CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr (CategoryTheory.Limits.pushoutAssoc g₁ g₂ g₃ g₄).hom = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pushout.inr CategoryTheory.Limits.pushout.inr
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                                                                                                                                                                                                  HasPushouts represents a choice of pushout for every pair of morphisms

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                                                                                                                                                                                                    If C has all limits of diagrams cospan f g, then it has all pullbacks

                                                                                                                                                                                                    If C has all colimits of diagrams span f g, then it has all pushouts

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                                                                                                                                                                                                    theorem CategoryTheory.Limits.baseChange_obj_hom {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.Limits.HasPullbacks C] {X : C} {Y : C} (f : X Y) (g : CategoryTheory.Over Y) :
                                                                                                                                                                                                    ((CategoryTheory.Limits.baseChange f).obj g).hom = CategoryTheory.Limits.pullback.snd

                                                                                                                                                                                                    Given a morphism f : X ⟶ Y, we can take morphisms over Y to morphisms over X via pullbacks. This is right adjoint to over.map (TODO)

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