Topological groups #
This file defines the following typeclasses:
IsTopologicalGroup
,IsTopologicalAddGroup
: multiplicative and additive topological groups, i.e., groups with continuous(*)
and(⁻¹)
/(+)
and(-)
;ContinuousSub G
means thatG
has a continuous subtraction operation.
There is an instance deducing ContinuousSub
from IsTopologicalGroup
but we use a separate
typeclass because, e.g., ℕ
and ℝ≥0
have continuous subtraction but are not additive groups.
We also define Homeomorph
versions of several Equiv
s: Homeomorph.mulLeft
,
Homeomorph.mulRight
, Homeomorph.inv
, and prove a few facts about neighbourhood filters in
groups.
Tags #
topological space, group, topological group
Groups with continuous multiplication #
In this section we prove a few statements about groups with continuous (*)
.
Multiplication from the left in a topological group as a homeomorphism.
Equations
- Homeomorph.mulLeft a = { toEquiv := Equiv.mulLeft a, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
Addition from the left in a topological additive group as a homeomorphism.
Equations
- Homeomorph.addLeft a = { toEquiv := Equiv.addLeft a, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
Multiplication from the right in a topological group as a homeomorphism.
Equations
- Homeomorph.mulRight a = { toEquiv := Equiv.mulRight a, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
Addition from the right in a topological additive group as a homeomorphism.
Equations
- Homeomorph.addRight a = { toEquiv := Equiv.addRight a, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
A version of Pi.continuousInv
for non-dependent functions. It is needed because sometimes
Lean fails to use Pi.continuousInv
for non-dependent functions.
A version of Pi.continuousNeg
for non-dependent functions. It is needed
because sometimes Lean fails to use Pi.continuousNeg
for non-dependent functions.
Inversion in a topological group as a homeomorphism.
Equations
- Homeomorph.inv G = { toEquiv := Equiv.inv G, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
Negation in a topological group as a homeomorphism.
Equations
- Homeomorph.neg G = { toEquiv := Equiv.neg G, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
Alias of the forward direction of continuous_inv_iff
.
Alias of the forward direction of continuousAt_inv_iff
.
Alias of the forward direction of continuousOn_inv_iff
.
Alias of Topology.IsInducing.continuousInv
.
Topological groups #
A topological group is a group in which the multiplication and inversion operations are
continuous. Topological additive groups are defined in the same way. Equivalently, we can require
that the division operation x y ↦ x * y⁻¹
(resp., subtraction) is continuous.
Conjugation is jointly continuous on G × G
when both mul
and inv
are continuous.
Conjugation is jointly continuous on G × G
when both add
and neg
are continuous.
Alias of IsTopologicalAddGroup.continuous_addConj_prod
.
Conjugation is jointly continuous on G × G
when both add
and neg
are continuous.
Conjugation by a fixed element is continuous when mul
is continuous.
Conjugation by a fixed element is continuous when add
is continuous.
Conjugation acting on fixed element of the group is continuous when both mul
and
inv
are continuous.
Conjugation acting on fixed element of the additive group is continuous when both
add
and neg
are continuous.
Alias of tendsto_neg_nhdsGT
.
Alias of tendsto_inv_nhdsGT
.
Alias of tendsto_neg_nhdsLT
.
Alias of tendsto_inv_nhdsLT
.
Alias of tendsto_neg_nhdsGT_neg
.
Alias of tendsto_inv_nhdsGT_inv
.
Alias of tendsto_neg_nhdsLT_neg
.
Alias of tendsto_inv_nhdsLT_inv
.
Alias of tendsto_neg_nhdsGE
.
Alias of tendsto_inv_nhdsGE
.
Alias of tendsto_neg_nhdsLE
.
Alias of tendsto_inv_nhdsLE
.
Alias of tendsto_neg_nhdsGE_neg
.
Alias of tendsto_inv_nhdsGE_inv
.
Alias of tendsto_neg_nhdsLE_neg
.
Alias of tendsto_inv_nhdsLE_inv
.
If multiplication is continuous in α
, then it also is in αᵐᵒᵖ
.
If addition is continuous in α
, then it also is in αᵃᵒᵖ
.
The map (x, y) ↦ (x, x * y)
as a homeomorphism. This is a shear mapping.
Equations
- Homeomorph.shearMulRight G = { toEquiv := (Equiv.refl G).prodShear Equiv.mulLeft, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
The map (x, y) ↦ (x, x + y)
as a homeomorphism. This is a shear mapping.
Equations
- Homeomorph.shearAddRight G = { toEquiv := (Equiv.refl G).prodShear Equiv.addLeft, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
Alias of Topology.IsInducing.topologicalGroup
.
The (topological-space) closure of a subgroup of a topological group is itself a subgroup.
Equations
- s.topologicalClosure = { carrier := closure ↑s, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
Instances For
The (topological-space) closure of an additive subgroup of an additive topological group is itself an additive subgroup.
Equations
- s.topologicalClosure = { carrier := closure ↑s, add_mem' := ⋯, zero_mem' := ⋯, neg_mem' := ⋯ }
Instances For
The topological closure of a normal subgroup is normal.
The topological closure of a normal additive subgroup is normal.
The connected component of 1 is a subgroup of G
.
Equations
- Subgroup.connectedComponentOfOne G = { carrier := connectedComponent 1, mul_mem' := ⋯, one_mem' := ⋯, inv_mem' := ⋯ }
Instances For
The connected component of 0 is a subgroup of G
.
Equations
- AddSubgroup.connectedComponentOfZero G = { carrier := connectedComponent 0, add_mem' := ⋯, zero_mem' := ⋯, neg_mem' := ⋯ }
Instances For
If a subgroup of a topological group is commutative, then so is its topological closure.
See note [reducible non-instances].
Equations
- s.commGroupTopologicalClosure hs = { toGroup := s.topologicalClosure.toGroup, mul_comm := ⋯ }
Instances For
If a subgroup of an additive topological group is commutative, then so is its topological closure.
See note [reducible non-instances].
Equations
- s.addCommGroupTopologicalClosure hs = { toAddGroup := s.topologicalClosure.toAddGroup, add_comm := ⋯ }
Instances For
A monoid homomorphism (a bundled morphism of a type that implements MonoidHomClass
) from a
topological group to a topological monoid is continuous provided that it is continuous at one. See
also uniformContinuous_of_continuousAt_one
.
An additive monoid homomorphism (a bundled morphism of a type that implements
AddMonoidHomClass
) from an additive topological group to an additive topological monoid is
continuous provided that it is continuous at zero. See also
uniformContinuous_of_continuousAt_zero
.
Let A
and B
be topological groups, and let φ : A → B
be a continuous surjective group
homomorphism. Assume furthermore that φ
is a quotient map (i.e., V ⊆ B
is open iff φ⁻¹ V
is open). Then φ
is an open quotient map, and in particular an open map.
Let A
and B
be topological additive groups, and let φ : A → B
be a continuous
surjective additive group homomorphism. Assume furthermore that φ
is a quotient map (i.e., V ⊆ B
is open iff φ⁻¹ V
is open). Then φ
is an open quotient map, and in particular an open map.
Any first countable topological group has an antitone neighborhood basis u : ℕ → Set G
for
which (u (n + 1)) ^ 2 ⊆ u n
. The existence of such a neighborhood basis is a key tool for
QuotientGroup.completeSpace
Any first countable topological additive group has an antitone neighborhood basis
u : ℕ → set G
for which u (n + 1) + u (n + 1) ⊆ u n
.
The existence of such a neighborhood basis is a key tool for QuotientAddGroup.completeSpace
A version of Homeomorph.mulLeft a b⁻¹
that is defeq to a / b
.
Equations
- Homeomorph.divLeft x = { toEquiv := Equiv.divLeft x, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
A version of Homeomorph.addLeft a (-b)
that is defeq to a - b
.
Equations
- Homeomorph.subLeft x = { toEquiv := Equiv.subLeft x, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
A version of Homeomorph.mulRight a⁻¹ b
that is defeq to b / a
.
Equations
- Homeomorph.divRight x = { toEquiv := Equiv.divRight x, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
A version of Homeomorph.addRight (-a) b
that is defeq to b - a
.
Equations
- Homeomorph.subRight x = { toEquiv := Equiv.subRight x, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
A subgroup S
of a topological group G
acts on G
properly discontinuously on the left, if
it is discrete in the sense that S ∩ K
is finite for all compact K
. (See also
DiscreteTopology
.)
A subgroup S
of an additive topological group G
acts on G
properly
discontinuously on the left, if it is discrete in the sense that S ∩ K
is finite for all compact
K
. (See also DiscreteTopology
.
A subgroup S
of a topological group G
acts on G
properly discontinuously on the right, if
it is discrete in the sense that S ∩ K
is finite for all compact K
. (See also
DiscreteTopology
.)
If G
is Hausdorff, this can be combined with t2Space_of_properlyDiscontinuousSMul_of_t2Space
to show that the quotient group G ⧸ S
is Hausdorff.
A subgroup S
of an additive topological group G
acts on G
properly discontinuously
on the right, if it is discrete in the sense that S ∩ K
is finite for all compact K
.
(See also DiscreteTopology
.)
If G
is Hausdorff, this can be combined with t2Space_of_properlyDiscontinuousVAdd_of_t2Space
to show that the quotient group G ⧸ S
is Hausdorff.
Some results about an open set containing the product of two sets in a topological group.
Given a compact set K
inside an open set U
, there is an open neighborhood V
of 1
such that K * V ⊆ U
.
Given a compact set K
inside an open set U
, there is an open neighborhood V
of
0
such that K + V ⊆ U
.
Given a compact set K
inside an open set U
, there is an open neighborhood V
of 1
such that V * K ⊆ U
.
Given a compact set K
inside an open set U
, there is an open neighborhood V
of
0
such that V + K ⊆ U
.
A compact set is covered by finitely many left multiplicative translates of a set with non-empty interior.
A compact set is covered by finitely many left additive translates of a set with non-empty interior.
Every weakly locally compact separable topological group is σ-compact. Note: this is not true if we drop the topological group hypothesis.
Every weakly locally compact separable topological additive group is σ-compact. Note: this is not true if we drop the topological group hypothesis.
Given two compact sets in a noncompact topological group, there is a translate of the second one that is disjoint from the first one.
Given two compact sets in a noncompact additive topological group, there is a translate of the second one that is disjoint from the first one.
On a topological group, 𝓝 : G → Filter G
can be promoted to a MulHom
.
Equations
- nhdsMulHom = { toFun := nhds, map_mul' := ⋯ }
Instances For
On an additive topological group, 𝓝 : G → Filter G
can be promoted to an AddHom
.
Equations
- nhdsAddHom = { toFun := nhds, map_add' := ⋯ }
Instances For
If G
is a group with topological ⁻¹
, then it is homeomorphic to its units.
Equations
- toUnits_homeomorph = { toEquiv := toUnits.toEquiv, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
If G
is an additive group with topological negation, then it is homeomorphic to
its additive units.
Equations
- toAddUnits_homeomorph = { toEquiv := toAddUnits.toEquiv, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
Alias of Units.isEmbedding_val
.
The topological group isomorphism between the units of a product of two monoids, and the product of the units of each monoid.
Equations
- Homeomorph.prodUnits = { toEquiv := MulEquiv.prodUnits.toEquiv, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
The topological group isomorphism between the additive units of a product of two additive monoids, and the product of the additive units of each additive monoid.
Equations
- Homeomorph.prodAddUnits = { toEquiv := AddEquiv.prodAddUnits.toEquiv, continuous_toFun := ⋯, continuous_invFun := ⋯ }
Instances For
Alias of Homeomorph.prodAddUnits
.
The topological group isomorphism between the additive units of a product of two additive monoids, and the product of the additive units of each additive monoid.
Equations
Instances For
Alias of Homeomorph.prodUnits
.
The topological group isomorphism between the units of a product of two monoids, and the product of the units of each monoid.