Monoids of endomorphisms, groups of automorphisms #
This file defines
- the endomorphism monoid structure on
Function.End α := α → α - the endomorphism monoid structure on
Monoid.End M := M →* MandAddMonoid.End M := M →+ M - the automorphism group structure on
Equiv.Perm α := α ≃ α - the automorphism group structure on
MulAut M := M ≃* MandAddAut M := M ≃+ M.
Implementation notes #
The definition of multiplication in the endomorphism monoids and automorphism groups agrees with
function composition, and multiplication in CategoryTheory.End, but not with
CategoryTheory.comp.
Tags #
end monoid, aut group
Type endomorphisms #
The monoid of endomorphisms.
Note that this is generalized by CategoryTheory.End to categories other than Type u.
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Monoid endomorphisms #
The permutation of a type is equivalent to the units group of the endomorphisms monoid of this type.
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Lift a monoid homomorphism f : G →* Function.End α to a monoid homomorphism
f : G →* Equiv.Perm α.
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Lemmas about mixing Perm with Equiv. Because we have multiple ways to express
Equiv.refl, Equiv.symm, and Equiv.trans, we want simp lemmas for every combination.
The assumption made here is that if you're using the group structure, you want to preserve it after
simp.
Lemmas about Equiv.Perm.sumCongr re-expressed via the group structure.
Equiv.Perm.sumCongr as a MonoidHom, with its two arguments bundled into a single Prod.
This is particularly useful for its MonoidHom.range projection, which is the subgroup of
permutations which do not exchange elements between α and β.
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Lemmas about Equiv.Perm.sigmaCongrRight re-expressed via the group structure.
Equiv.Perm.sigmaCongrRight as a MonoidHom.
This is particularly useful for its MonoidHom.range projection, which is the subgroup of
permutations which do not exchange elements between fibers.
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Lemmas about Equiv.Perm.extendDomain re-expressed via the group structure.
The inclusion map of permutations on a subtype of α into permutations of α,
fixing the other points.
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Left-multiplying a permutation with swap i j twice gives the original permutation.
This specialization of swap_mul_self is useful when using cosets of permutations.
Right-multiplying a permutation with swap i j twice gives the original permutation.
This specialization of swap_mul_self is useful when using cosets of permutations.
A stronger version of mul_right_injective
A stronger version of mul_left_injective
The group operation on multiplicative automorphisms is defined by g h => MulEquiv.trans h g.
This means that multiplication agrees with composition, (g*h)(x) = g (h x).
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Monoid hom from the group of multiplicative automorphisms to the group of permutations.
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Group conjugation, MulAut.conj g h = g * h * g⁻¹, as a monoid homomorphism
mapping multiplication in G into multiplication in the automorphism group MulAut G.
See also the type ConjAct G for any group G, which has a MulAction (ConjAct G) G instance
where conj G acts on G by conjugation.
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The group operation on additive automorphisms is defined by g h => AddEquiv.trans h g.
This means that multiplication agrees with composition, (g*h)(x) = g (h x).
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Monoid hom from the group of multiplicative automorphisms to the group of permutations.
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Additive group conjugation, AddAut.conj g h = g + h - g, as an additive monoid
homomorphism mapping addition in G into multiplication in the automorphism group AddAut G
(written additively in order to define the map).