The University of Michigan Combinatorics Seminar


Abstract 

Work of Aguiar, Bergeron, and Sottile established the category of "combinatorial Hopf algebras" and showed that the quasisymmetric functions are the terminal object in this category. Stembridge's peak functions form a special Hopf subalgebra of the quasisymmetric functions called the "odd" subalgebra; moreover, the algebra of peak functions is terminal in the category of odd combinatorial Hopf algebras. 