Superization and (q, t)-Specialization in Combinatorial Hopf Algebras

We extend a classical construction on symmetric functions, the superization process, to several combinatorial Hopf algebras, and obtain analogs of the hook-content formula for the (q, t)-specializations of various bases. Exploiting the dendriform structures yields in particular (q, t)-analogs of the Björner-Wachs q-hook-length formulas for binary trees, and similar formulas for plane trees.