Combinatorial Hopf species and algebras from preorder cuts (2301.06479v1)

Abstract: We introduce new concepts and viewpoints on combinatorial Hopf species and algebras. We give a category ${\rm \bf set_{\mathbb{N}}}$ whose objects are sets, and (dualizable) morphisms represented by matrices of non-negative integers. For a bimonoid species $(B,\Delta, \mu)$ in ${\rm \bf set_{\mathbb{N}}}$ we may then dualize the product $\mu$ to get two intertwined coproducts $\Delta, \Delta^\prime$. We consider restriction species $\mathsf{S}$ over ${\rm \bf set_{\mathbb{N}}}$ accompanied by pairs of natural transformations $\pi_1, \pi_2 : \mathsf{S} \rightarrow {\rm Pre}$ to the species of preorders. A simple construction associates two comonoid species $\Delta^1$ and $\Delta^2$, and we investigate when they are intertwined. We get new Hopf algebras: i. choosing an arbitrary set of permutations without global descents, we get associated a quotient Hopf algebra of the Malvenuto-Reutenauer Hopf algebra of permutations avoiding this chosen set, ii. a Hopf algebra of pairs of parking filtrations, and iii. three Hopf algebras of pairs of preorders.