Pointwise operations on filters #
This file defines pointwise operations on filters. This is useful because usual algebraic operations distribute over pointwise operations. For example,
(f₁ * f₂).map m = f₁.map m * f₂.map m𝓝 (x * y) = 𝓝 x * 𝓝 y
Main declarations #
0(Filter.instZero): Pure filter at0 : α, or alternatively principal filter at0 : Set α.1(Filter.instOne): Pure filter at1 : α, or alternatively principal filter at1 : Set α.f + g(Filter.instAdd): Addition, filter generated by alls + twheres ∈ fandt ∈ g.f * g(Filter.instMul): Multiplication, filter generated by alls * twheres ∈ fandt ∈ g.-f(Filter.instNeg): Negation, filter of all-swheres ∈ f.f⁻¹(Filter.instInv): Inversion, filter of alls⁻¹wheres ∈ f.f - g(Filter.instSub): Subtraction, filter generated by alls - twheres ∈ fandt ∈ g.f / g(Filter.instDiv): Division, filter generated by alls / twheres ∈ fandt ∈ g.f +ᵥ g(Filter.instVAdd): Scalar addition, filter generated by alls +ᵥ twheres ∈ fandt ∈ g.f -ᵥ g(Filter.instVSub): Scalar subtraction, filter generated by alls -ᵥ twheres ∈ fandt ∈ g.f • g(Filter.instSMul): Scalar multiplication, filter generated by alls • twheres ∈ fandt ∈ g.a +ᵥ f(Filter.instVAddFilter): Translation, filter of alla +ᵥ swheres ∈ f.a • f(Filter.instSMulFilter): Scaling, filter of alla • swheres ∈ f.
For α a semigroup/monoid, Filter α is a semigroup/monoid.
As an unfortunate side effect, this means that n • f, where n : ℕ, is ambiguous between
pointwise scaling and repeated pointwise addition. See note [pointwise nat action].
Implementation notes #
We put all instances in the locale Pointwise, so that these instances are not available by
default. Note that we do not mark them as reducible (as argued by note [reducible non-instances])
since we expect the locale to be open whenever the instances are actually used (and making the
instances reducible changes the behavior of simp).
Tags #
filter multiplication, filter addition, pointwise addition, pointwise multiplication,
0/1 as filters #
Filter negation/inversion #
The negation of a filter is the pointwise preimage under - of its sets.
Equations
- Filter.instNeg = { neg := Filter.map Neg.neg }
The inverse of a filter is the pointwise preimage under ⁻¹ of its sets.
Equations
- Filter.instInv = { inv := Filter.map Inv.inv }
Negation is involutive on Filter α if it is on α.
Equations
- Filter.instInvolutiveNeg = let src := Filter.instNeg; InvolutiveNeg.mk (_ : ∀ (f : Filter α), Filter.map Neg.neg (Filter.map Neg.neg f) = f)
Instances For
Inversion is involutive on Filter α if it is on α.
Equations
- Filter.instInvolutiveInv = let src := Filter.instInv; InvolutiveInv.mk (_ : ∀ (f : Filter α), Filter.map Inv.inv (Filter.map Inv.inv f) = f)
Instances For
Filter addition/multiplication #
Filter subtraction/division #
Repeated pointwise multiplication/division (not the same as pointwise repeated
multiplication/division!) of a Filter. See Note [pointwise nat action].
Instances For
Filter α is an AddSemigroup under pointwise operations if α is.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Filter α is an AddCommSemigroup under pointwise operations if α is.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Filter α is a CommSemigroup under pointwise operations if α is.
Equations
- Filter.commSemigroup = let src := Filter.semigroup; CommSemigroup.mk (_ : ∀ (x x_1 : Filter α), Filter.map₂ (fun x x_2 => x * x_2) x x_1 = Filter.map₂ (fun x x_2 => x * x_2) x_1 x)
Instances For
Filter α is an AddZeroClass under pointwise operations if α is.
Equations
- Filter.addZeroClass = AddZeroClass.mk (_ : ∀ (l : Filter α), Filter.map₂ (fun x x_1 => x + x_1) (pure 0) l = l) (_ : ∀ (l : Filter α), Filter.map₂ (fun x x_1 => x + x_1) l (pure 0) = l)
Instances For
Filter α is a MulOneClass under pointwise operations if α is.
Equations
- Filter.mulOneClass = MulOneClass.mk (_ : ∀ (l : Filter α), Filter.map₂ (fun x x_1 => x * x_1) (pure 1) l = l) (_ : ∀ (l : Filter α), Filter.map₂ (fun x x_1 => x * x_1) l (pure 1) = l)
Instances For
If φ : α →+ β then mapAddMonoidHom φ is the monoid homomorphism
Filter α →+ Filter β induced by map φ.
Equations
- One or more equations did not get rendered due to their size.
Instances For
If φ : α →* β then mapMonoidHom φ is the monoid homomorphism
Filter α →* Filter β induced by map φ.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Equations
- One or more equations did not get rendered due to their size.
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pure as an AddMonoidHom.
Equations
- One or more equations did not get rendered due to their size.
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pure as a MonoidHom.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Equations
- Filter.nsmul_mem_nsmul.match_1 motive x h_1 h_2 = Nat.casesOn x (h_1 ()) fun n => h_2 n
Instances For
Equations
- Filter.nsmul_top.match_1 motive x h_1 h_2 h_3 = Nat.casesOn x (h_1 ()) fun n => Nat.casesOn n (h_2 ()) fun n => h_3 n
Instances For
Filter α is a subtraction monoid under pointwise operations if
α is.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Filter α is a division monoid under pointwise operations if α is.
Equations
- One or more equations did not get rendered due to their size.
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Filter α is a commutative subtraction monoid under pointwise operations if α is.
Equations
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Filter α has distributive negation if α has.
Equations
- One or more equations did not get rendered due to their size.
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Note that Filter is not a MulZeroClass because 0 * ⊥ ≠ 0.
Note that Filter α is not a group because f / f ≠ 1 in general
Scalar addition/multiplication of filters #
Scalar subtraction of filters #
Translation/scaling of filters #
a +ᵥ f is the map of f under a +ᵥ in locale Pointwise.
Equations
- Filter.instVAddFilter = { vadd := fun a => Filter.map ((fun x x_1 => x +ᵥ x_1) a) }
Instances For
a • f is the map of f under a • in locale Pointwise.
Equations
- Filter.instSMulFilter = { smul := fun a => Filter.map ((fun x x_1 => x • x_1) a) }
Instances For
A distributive multiplicative action of a monoid on an additive monoid β gives a distributive
multiplicative action on Filter β.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A multiplicative action of a monoid on a monoid β gives a multiplicative action on Set β.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Note that we have neither SMulWithZero α (Filter β) nor SMulWithZero (Filter α) (Filter β)
because 0 * ⊥ ≠ 0.