Uniform structure on topological groups #
This file defines uniform groups and its additive counterpart. These typeclasses should be
preferred over using [TopologicalSpace α] [TopologicalGroup α]
since every topological
group naturally induces a uniform structure.
Main declarations #
UniformGroup
andUniformAddGroup
: Multiplicative and additive uniform groups, that i.e., groups with uniformly continuous(*)
and(⁻¹)
/(+)
and(-)
.
Main results #
-
TopologicalAddGroup.toUniformSpace
andcomm_topologicalAddGroup_is_uniform
can be used to construct a canonical uniformity for a topological add group. -
extension of ℤ-bilinear maps to complete groups (useful for ring completions)
-
QuotientGroup.completeSpace
andQuotientAddGroup.completeSpace
guarantee that quotients of first countable topological groups by normal subgroups are themselves complete. In particular, the quotient of a Banach space by a subspace is complete.
- uniformContinuous_div : UniformContinuous fun p => p.fst / p.snd
A uniform group is a group in which multiplication and inversion are uniformly continuous.
Instances
- uniformContinuous_sub : UniformContinuous fun p => p.fst - p.snd
A uniform additive group is an additive group in which addition and negation are uniformly continuous.
Instances
Equations
- UniformContinuous.const_nsmul.match_1 motive x h_1 h_2 = Nat.casesOn x (h_1 ()) fun n => h_2 n
Instances For
Equations
- UniformContinuous.const_zsmul.match_1 motive x h_1 h_2 = Int.casesOn x (fun a => h_1 a) fun a => h_2 a
Instances For
An additive group homomorphism (a bundled morphism of a type that implements
AddMonoidHomClass
) between two uniform additive groups is uniformly continuous provided that it
is continuous at zero. See also continuous_of_continuousAt_zero
.
A group homomorphism (a bundled morphism of a type that implements MonoidHomClass
) between
two uniform groups is uniformly continuous provided that it is continuous at one. See also
continuous_of_continuousAt_one
.
A homomorphism from a uniform additive group to a discrete uniform additive group is continuous if and only if its kernel is open.
A homomorphism from a uniform group to a discrete uniform group is continuous if and only if its kernel is open.
The right uniformity on a topological additive group (as opposed to the left uniformity).
Warning: in general the right and left uniformities do not coincide and so one does not obtain a
UniformAddGroup
structure. Two important special cases where they do coincide are for
commutative additive groups (see comm_topologicalAddGroup_is_uniform
) and for compact
additive groups (see topologicalAddGroup_is_uniform_of_compactSpace
).
Equations
- One or more equations did not get rendered due to their size.
Instances For
The right uniformity on a topological group (as opposed to the left uniformity).
Warning: in general the right and left uniformities do not coincide and so one does not obtain a
UniformGroup
structure. Two important special cases where they do coincide are for
commutative groups (see comm_topologicalGroup_is_uniform
) and for compact groups (see
topologicalGroup_is_uniform_of_compactSpace
).
Equations
- One or more equations did not get rendered due to their size.
Instances For
Equations
- TopologicalAddGroup.tendstoUniformly_iff.match_1 x motive x h_1 = Exists.casesOn x fun w h => And.casesOn h fun left right => h_1 w left right
Instances For
Equations
- TopologicalAddGroup.tendstoLocallyUniformly_iff.match_1 F f p x u x motive x h_1 = And.casesOn x fun left right => h_1 left right
Instances For
Equations
- TopologicalAddGroup.tendstoLocallyUniformlyOn_iff.match_1 F f p s x u x motive x h_1 = And.casesOn x fun left right => h_1 left right
Instances For
Bourbaki GT III.6.5 Theorem I: ℤ-bilinear continuous maps from dense images into a complete Hausdorff group extend by continuity. Note: Bourbaki assumes that α and β are also complete Hausdorff, but this is not necessary.
The quotient G ⧸ N
of a complete first countable topological additive group
G
by a normal additive subgroup is itself complete. Consequently, quotients of Banach spaces by
subspaces are complete. [N. Bourbaki, General Topology, IX.3.1 Proposition 4][bourbaki1966b]
Because an additive topological group is not equipped with a UniformSpace
instance by default,
we must explicitly provide it in order to consider completeness. See
QuotientAddGroup.completeSpace
for a version in which G
is already equipped with a uniform
structure.
The quotient G ⧸ N
of a complete first countable topological group G
by a normal subgroup
is itself complete. [N. Bourbaki, General Topology, IX.3.1 Proposition 4][bourbaki1966b]
Because a topological group is not equipped with a UniformSpace
instance by default, we must
explicitly provide it in order to consider completeness. See QuotientGroup.completeSpace
for a
version in which G
is already equipped with a uniform structure.
The quotient G ⧸ N
of a complete first countable uniform additive group
G
by a normal additive subgroup is itself complete. Consequently, quotients of Banach spaces by
subspaces are complete. In contrast to QuotientAddGroup.completeSpace'
, in this version
G
is already equipped with a uniform structure.
[N. Bourbaki, General Topology, IX.3.1 Proposition 4][bourbaki1966b]
Even though G
is equipped with a uniform structure, the quotient G ⧸ N
does not inherit a
uniform structure, so it is still provided manually via TopologicalAddGroup.toUniformSpace
.
In the most common use case ─ quotients of normed additive commutative groups by subgroups ─
significant care was taken so that the uniform structure inherent in that setting coincides
(definitionally) with the uniform structure provided here.
The quotient G ⧸ N
of a complete first countable uniform group G
by a normal subgroup
is itself complete. In contrast to QuotientGroup.completeSpace'
, in this version G
is
already equipped with a uniform structure.
[N. Bourbaki, General Topology, IX.3.1 Proposition 4][bourbaki1966b]
Even though G
is equipped with a uniform structure, the quotient G ⧸ N
does not inherit a
uniform structure, so it is still provided manually via TopologicalGroup.toUniformSpace
.
In the most common use cases, this coincides (definitionally) with the uniform structure on the
quotient obtained via other means.