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HopfAlgebras.Algebra.PlanarForest

The Algebra of Ordered Planar Forests #

This file defines the noncommutative algebra freely spanned by ordered planar forests. Multiplication is concatenation of ordered forests. The quotient maps to the existing commutative non-planar forest algebras forget sibling order.

This is the algebraic carrier needed for ordered-tree Hopf algebras such as the Munthe-Kaas-Wright Hopf algebra.

Main definitions #

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The noncommutative algebra freely spanned by ordered planar forests.

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    The monomial associated to an ordered planar forest.

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      The counit value on an ordered forest monomial.

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        The counit algebra homomorphism, sending the empty ordered forest to 1.

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          Forget planar order as an algebra morphism to the commutative forest algebra.

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            Algebra characters on the ordered planar forest algebra.

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              Evaluate a character on the monomial associated to an ordered planar forest.

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                theorem HopfAlgebras.PlanarForestAlgebra.Character.ext {R : Type u} [CommSemiring R] {χ ψ : Character R} (h : ∀ (ts : PlanarForest), χ.evalForest ts = ψ.evalForest ts) :
                χ = ψ
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                abbrev HopfAlgebras.LPlanarForestAlgebra (α : Type u) (R : Type v) [Semiring R] :
                Type (max u v)

                The noncommutative algebra freely spanned by labelled ordered planar forests.

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                  theorem HopfAlgebras.LPlanarForest.constLabel_append {α : Type u} (a : α) (ts us : PlanarForest) :
                  constLabel a (ts ++ us) = constLabel a ts ++ constLabel a us

                  The monomial associated to a labelled ordered planar forest.

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                    The counit value on a labelled ordered forest monomial.

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                      theorem HopfAlgebras.LPlanarForestAlgebra.counitCoeff_ne_nil {α : Type u} {R : Type v} [Zero R] [One R] {ts : LPlanarForest α} (hts : ts []) :
                      theorem HopfAlgebras.LPlanarForestAlgebra.counitCoeff_map {α : Type u} {β : Type w} {R : Type v} [Zero R] [One R] (f : αβ) (ts : LPlanarForest α) :

                      The counit algebra homomorphism, sending the empty ordered forest to 1.

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                        theorem HopfAlgebras.LPlanarForestAlgebra.counit_ofForest_ne_nil {α : Type u} {R : Type v} [CommSemiring R] {ts : LPlanarForest α} (hts : ts []) :
                        (counit α R) (ofForest ts) = 0

                        Forget labels as an algebra morphism between ordered planar forest algebras.

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                          Label every vertex by a fixed label as an algebra morphism.

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                            noncomputable def HopfAlgebras.LPlanarForestAlgebra.mapLabels {α : Type u} {β : Type w} (R : Type v) [CommSemiring R] (f : αβ) :

                            Relabel ordered planar forests as an algebra morphism.

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                              theorem HopfAlgebras.LPlanarForestAlgebra.mapLabels_ofForest {α : Type u} {β : Type w} {R : Type v} [CommSemiring R] (f : αβ) (ts : LPlanarForest α) :
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                              theorem HopfAlgebras.LPlanarForestAlgebra.mapLabels_comp {α : Type u} {β : Type w} {γ : Type x} {R : Type v} [CommSemiring R] (g : βγ) (f : αβ) :
                              (mapLabels R g).comp (mapLabels R f) = mapLabels R (g f)

                              Forget planar order as an algebra morphism to the commutative labelled forest algebra.

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                                theorem HopfAlgebras.LPlanarForestAlgebra.mapLabels_comp_constLabel {α : Type u} {β : Type w} {R : Type v} [CommSemiring R] (f : αβ) (a : α) :
                                (mapLabels R f).comp (constLabel a R) = constLabel (f a) R
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                                Algebra characters on the labelled ordered planar forest algebra.

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                                  noncomputable def HopfAlgebras.LPlanarForestAlgebra.Character.evalForest {α : Type u} {R : Type v} [CommSemiring R] (χ : Character α R) (ts : LPlanarForest α) :
                                  R

                                  Evaluate a character on the monomial associated to a labelled ordered planar forest.

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                                    theorem HopfAlgebras.LPlanarForestAlgebra.Character.ext {α : Type u} {R : Type v} [CommSemiring R] {χ ψ : Character α R} (h : ∀ (ts : LPlanarForest α), χ.evalForest ts = ψ.evalForest ts) :
                                    χ = ψ
                                    theorem HopfAlgebras.LPlanarForestAlgebra.Character.ext_iff {α : Type u} {R : Type v} [CommSemiring R] {χ ψ : Character α R} :
                                    χ = ψ ∀ (ts : LPlanarForest α), χ.evalForest ts = ψ.evalForest ts

                                    Pull a labelled commutative forest character back by forgetting planar order.

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                                      Pull an unlabelled ordered planar forest character back by forgetting labels.

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                                        Pull a labelled ordered planar forest character back along constant labelling.

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                                          noncomputable def HopfAlgebras.LPlanarForestAlgebra.Character.comapMapLabels {α : Type u} {β : Type w} {R : Type v} [CommSemiring R] (f : αβ) (χ : Character β R) :

                                          Pull a labelled ordered planar forest character back along relabelling.

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                                            theorem HopfAlgebras.LPlanarForestAlgebra.Character.comapMapLabels_id {α : Type u} {R : Type v} [CommSemiring R] (χ : Character α R) :
                                            comapMapLabels (fun (a : α) => a) χ = χ
                                            theorem HopfAlgebras.LPlanarForestAlgebra.Character.comapMapLabels_comp {α : Type u} {β : Type w} {γ : Type x} {R : Type v} [CommSemiring R] (g : βγ) (f : αβ) (χ : Character γ R) :