The bialgebra structure on monoid algebras #
Given a monoid M, a commutative semiring R and an R-bialgebra A, this file collects results
about the R-bialgebra instance on A[M] inherited from the corresponding structure on its
coefficients, building upon results in Mathlib/RingTheory/Coalgebra/MonoidAlgebra.lean about the
coalgebra structure.
Main definitions #
(Add)MonoidAlgebra.instBialgebra: theR-bialgebra structure onA[M]whenMis an (add) monoid andAis anR-bialgebra.LaurentPolynomial.instBialgebra: theR-bialgebra structure on the Laurent polynomialsA[T;T⁻¹]whenAis anR-bialgebra.(Add)MonoidAlgebra.mapDomainBialgHomEquiv: isomorphism betweenR-bialgebra homsA[G] → A[H]and groups homsG → HwhenGandHare an (add) group andAis anR-bialgebra.
A group algebra is spanned by its group-like elements.
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If f : M → N is a monoid hom, then MonoidAlgebra.mapDomain f is a bialgebra hom between
their monoid algebras.
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If f : M → N is an additive monoid hom, then MonoidAlgebra.mapDomain f is a bialgebra hom
between their additive monoid algebras.
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A R-bialgebra homomorphism from A[M] is uniquely defined by its
values on the functions single m 1 and single 1 a.
See note [partially-applied ext lemmas]. Note that the first assumption isn't written as an
equality of MonoidHoms because of doesn't additivise.
A R-bialgebra homomorphism from A[M] is uniquely defined by its
values on the functions single m 1 and single 1 a.
See note [partially-applied ext lemmas]. Note that the first assumption isn't written as an
equality of AddMonoidHoms because of doesn't multiplicativise.
Version of bialgHom_ext where both assumptions are written as equalities of bundled homs.
Isomorphic monoids have isomorphic monoid algebras.
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- MonoidAlgebra.domCongrBialgEquiv R A e = BialgEquiv.ofAlgEquiv (MonoidAlgebra.domCongr R A e) ⋯ ⋯
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Isomorphic monoids have isomorphic monoid algebras.
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- AddMonoidAlgebra.domCongrBialgEquiv R A e = BialgEquiv.ofAlgEquiv (AddMonoidAlgebra.domCongr R A e) ⋯ ⋯
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The trivial monoid algebra is isomorphic to the base ring.
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The trivial monoid algebra is isomorphic to the base ring.
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The R-bialgebra map from the group algebra on the group-like elements of A to A.
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- MonoidAlgebra.liftGroupLikeBialgHom = BialgHom.ofAlgHom ((MonoidAlgebra.lift R A (GroupLike R A)) { toFun := fun (g : GroupLike R A) => ↑g, map_one' := ⋯, map_mul' := ⋯ }) ⋯ ⋯
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The bialgebra equivalence between MonoidAlgebra and AddMonoidAlgebra in terms of
Additive.
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MonoidAlgebra.lift as a MulEquiv.
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- MonoidAlgebra.liftMulEquiv R A M = { toEquiv := (MonoidAlgebra.lift R A M).trans (WithConv.equiv (MonoidAlgebra R M →ₐ[R] A)).symm, map_mul' := ⋯ }
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A bialgebra homomorphism R[G] → R[H] between group algebras over a domain R comes from a
group hom G → H.
See MonoidAlgebra.mapDomainBialgHom for the forward map.
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- MonoidAlgebra.mapDomainOfBialgHom f = { toFun := MonoidAlgebra.mapDomainOfBialgHomFun✝ f, map_one' := ⋯, map_mul' := ⋯ }
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A bialgebra homomorphism R[G] → R[H] between group algebras over a domain R comes from a
group hom G → H.
See MonoidAlgebra.mapDomainBialgHom for the forward map.
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- AddMonoidAlgebra.mapDomainOfBialgHom f = { toFun := AddMonoidAlgebra.mapDomainOfBialgHomFun✝ f, map_zero' := ⋯, map_add' := ⋯ }
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The equivalence between group homs G → H and bialgebra homs R[G] → R[H] of group algebras
over a domain.
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- MonoidAlgebra.mapDomainBialgHomEquiv = { toFun := MonoidAlgebra.mapDomainBialgHom R, invFun := MonoidAlgebra.mapDomainOfBialgHom, left_inv := ⋯, right_inv := ⋯ }
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The equivalence between group homs G → H and bialgebra homs R[G] → R[H] of group algebras
over a domain.
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- AddMonoidAlgebra.mapDomainBialgHomEquiv = { toFun := AddMonoidAlgebra.mapDomainBialgHom R, invFun := AddMonoidAlgebra.mapDomainOfBialgHom, left_inv := ⋯, right_inv := ⋯ }
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The group isomorphism between group homs G → H and bialgebra homs R[G] → R[H] of group
algebras over a domain.
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- MonoidAlgebra.mapDomainBialgHomMulEquiv = { toEquiv := MonoidAlgebra.mapDomainBialgHomEquiv.trans (WithConv.equiv (MonoidAlgebra R G →ₐc[R] MonoidAlgebra R H)).symm, map_mul' := ⋯ }
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See note [partially-applied ext lemmas].
The bialgebra equivalence between AddMonoidAlgebra and MonoidAlgebra in terms of
Multiplicative.
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AddMonoidAlgebra.lift as a MulEquiv.
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- AddMonoidAlgebra.liftMulEquiv R A M = { toEquiv := (AddMonoidAlgebra.lift R A M).trans (WithConv.equiv (AddMonoidAlgebra R M →ₐ[R] A)).symm, map_mul' := ⋯ }
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The group isomorphism between group homs G → H and bialgebra homs R[G] → R[H] of group
algebras over a domain.
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