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HopfAlgebras.Hopf.Coproduct

Coproduct Terms in the Forest Algebra #

This file turns the finite cut-term lists from HopfAlgebras.Cuts.Rooted into elements of the monoid algebra on pairs of rooted forests. This is a tensor-coded target for the BCK coproduct: a pair (φ, ψ) represents the basis tensor φ ⊗ ψ.

The tree coproduct is first defined for planar representatives, then quotiented to non-planar rooted trees and forests.

Main definitions #

References #

@[reducible, inline]

Tensor-coded forest algebra: (φ, ψ) represents the basis tensor φ ⊗ ψ.

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    The basis tensor represented by a pair of rooted forests.

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      @[simp]
      theorem HopfAlgebras.ForestTensorAlgebra.ofForests_add {R : Type u} [Semiring R] (φ₁ φ₂ ψ₁ ψ₂ : RootedForest) :
      ofForests (φ₁ + φ₂) (ψ₁ + ψ₂) = ofForests φ₁ ψ₁ * ofForests φ₂ ψ₂

      Sum a finite list of basis tensors. Duplicates contribute multiplicity.

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        Apply the counit to the left tensor factor.

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          Apply the counit to the right tensor factor.

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            @[reducible, inline]

            Triple tensor-coded forest algebra: (φ, ψ, η) represents the basis tensor φ ⊗ ψ ⊗ η.

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              The basis triple tensor represented by a triple of rooted forests.

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                @[simp]
                theorem HopfAlgebras.ForestTripleTensorAlgebra.ofForests_add {R : Type u} [Semiring R] (φ₁ φ₂ ψ₁ ψ₂ η₁ η₂ : RootedForest) :
                ofForests (φ₁ + φ₂) (ψ₁ + ψ₂) (η₁ + η₂) = ofForests φ₁ ψ₁ η₁ * ofForests φ₂ ψ₂ η₂

                Sum a finite list of basis triple tensors. Duplicates contribute multiplicity.

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                  Multiply two finite lists of triple tensor basis terms.

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                    Embed a pair tensor as the first two factors of a triple tensor.

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                      Embed a pair tensor as the last two factors of a triple tensor.

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                        noncomputable def HopfAlgebras.PTree.coproduct {R : Type u} [Semiring R] (t : PTree) :

                        The planar BCK coproduct of a tree, represented in the tensor-coded algebra.

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                          The reduced planar BCK coproduct, summing only proper cut terms.

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                            Multiplicative extension of the planar coproduct to planar forests.

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                              The BCK coproduct of a non-planar rooted tree.

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                                The reduced BCK coproduct of a non-planar rooted tree.

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                                  A finite representative list for the forest coproduct, using Quotient.out.

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                                    theorem HopfAlgebras.RootedForest.coproductTerms_left_eq_zero {φ : RootedForest} {term : RootedForest × RootedForest} (hterm : term φ.coproductTerms) (hleft : term.1 = 0) :
                                    term.2 = φ

                                    The only forest coproduct terms with empty left factor are 1 ⊗ φ.

                                    theorem HopfAlgebras.RootedForest.coproductTerms_right_eq_zero {φ : RootedForest} {term : RootedForest × RootedForest} (hterm : term φ.coproductTerms) (hright : term.2 = 0) :
                                    term.1 = φ

                                    The only forest coproduct terms with empty right factor are φ ⊗ 1.

                                    A finite representative list for the reduced forest coproduct.

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                                      The multiplicative coproduct of a non-planar rooted forest.

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                                        The reduced BCK coproduct of a non-planar rooted forest.

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                                          Apply the coproduct to the first tensor factor, the map Δ ⊗ id.

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                                            Apply the coproduct to the second tensor factor, the map id ⊗ Δ.

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                                                theorem HopfAlgebras.ForestTripleTensorAlgebra.coproductLeftTerms_order {terms : List (RootedForest × RootedForest)} {m : } (hterms : termterms, term.1.order + term.2.order = m) {triple : RootedForest × RootedForest × RootedForest} (htriple : triple coproductLeftTerms terms) :
                                                triple.1.order + triple.2.1.order + triple.2.2.order = m
                                                theorem HopfAlgebras.ForestTripleTensorAlgebra.coproductRightTerms_order {terms : List (RootedForest × RootedForest)} {m : } (hterms : termterms, term.1.order + term.2.order = m) {triple : RootedForest × RootedForest × RootedForest} (htriple : triple coproductRightTerms terms) :
                                                triple.1.order + triple.2.1.order + triple.2.2.order = m