Group actions by isometries #
In this file we define two typeclasses:
IsometricSMul M Xsays thatMmultiplicatively acts on a (pseudo extended) metric spaceXby isometries;IsometricVAddis an additive version ofIsometricSMul.
We also prove basic facts about isometric actions and define bundled isometries
IsometryEquiv.constSMul, IsometryEquiv.mulLeft, IsometryEquiv.mulRight,
IsometryEquiv.divLeft, IsometryEquiv.divRight, and IsometryEquiv.inv, as well as their
additive versions.
If G is a group, then IsometricSMul G G means that G has a left-invariant metric while
IsometricSMul Gᵐᵒᵖ G means that G has a right-invariant metric. For a commutative group,
these two notions are equivalent. A group with a right-invariant metric can be also represented as a
NormedGroup.
An additive action is isometric if each map x ↦ c +ᵥ x is an isometry.
Instances
A multiplicative action is isometric if each map x ↦ c • x is an isometry.
Instances
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- ⋯ = ⋯
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- ⋯ = ⋯
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- ⋯ = ⋯
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- ⋯ = ⋯
If an additive group G acts on X by isometries,
then IsometryEquiv.constVAdd is the isometry of X given by addition of a constant element of the
group.
Equations
- IsometryEquiv.constVAdd c = { toEquiv := AddAction.toPerm c, isometry_toFun := ⋯ }
Instances For
If a group G acts on X by isometries, then IsometryEquiv.constSMul is the isometry of
X given by multiplication of a constant element of the group.
Equations
- IsometryEquiv.constSMul c = { toEquiv := MulAction.toPerm c, isometry_toFun := ⋯ }
Instances For
Addition y ↦ x + y as an IsometryEquiv.
Equations
- IsometryEquiv.addLeft c = { toEquiv := Equiv.addLeft c, isometry_toFun := ⋯ }
Instances For
Multiplication y ↦ x * y as an IsometryEquiv.
Equations
- IsometryEquiv.mulLeft c = { toEquiv := Equiv.mulLeft c, isometry_toFun := ⋯ }
Instances For
Addition y ↦ y + x as an IsometryEquiv.
Equations
- IsometryEquiv.addRight c = { toEquiv := Equiv.addRight c, isometry_toFun := ⋯ }
Instances For
Multiplication y ↦ y * x as an IsometryEquiv.
Equations
- IsometryEquiv.mulRight c = { toEquiv := Equiv.mulRight c, isometry_toFun := ⋯ }
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Subtraction y ↦ y - x as an IsometryEquiv.
Equations
- IsometryEquiv.subRight c = { toEquiv := Equiv.subRight c, isometry_toFun := ⋯ }
Instances For
Division y ↦ y / x as an IsometryEquiv.
Equations
- IsometryEquiv.divRight c = { toEquiv := Equiv.divRight c, isometry_toFun := ⋯ }
Instances For
Subtraction y ↦ x - y as an IsometryEquiv.
Equations
- IsometryEquiv.subLeft c = { toEquiv := Equiv.subLeft c, isometry_toFun := ⋯ }
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Division y ↦ x / y as an IsometryEquiv.
Equations
- IsometryEquiv.divLeft c = { toEquiv := Equiv.divLeft c, isometry_toFun := ⋯ }
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Negation x ↦ -x as an IsometryEquiv.
Equations
- IsometryEquiv.neg G = { toEquiv := Equiv.neg G, isometry_toFun := ⋯ }
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Inversion x ↦ x⁻¹ as an IsometryEquiv.
Equations
- IsometryEquiv.inv G = { toEquiv := Equiv.inv G, isometry_toFun := ⋯ }
Instances For
Given an additive isometric action of G on X, the image of a bounded set in X
under translation by c : G is bounded
If G acts isometrically on X, then the image of a bounded set in X under scalar
multiplication by c : G is bounded. See also Bornology.IsBounded.smul₀ for a similar lemma about
normed spaces.
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- ⋯ = ⋯
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