Enumerative combinatorics
Journal of Algebraic Combinatorics: An International Journal
Order Structure on the Algebra of Permutations and of Planar Binary Trees
Journal of Algebraic Combinatorics: An International Journal
Commutative combinatorial Hopf algebras
Journal of Algebraic Combinatorics: An International Journal
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Consider the coradical filtrations of the Hopf algebras of planar binary trees of Loday and Ronco and of permutations of Malvenuto and Reutenauer. We give explicit isomorphisms showing that the associated graded Hopf algebras are dual to the cocommutative Hopf algebras introduced in the late 1980's by Grossman and Larson. These Hopf algebras are constructed from ordered trees and heap-ordered trees, respectively. These results follow from the fact that whenever one starts from a Hopf algebra that is a cofree graded coalgebra, the associated graded Hopf algebra is a shuffle Hopf algebra.