Transfer systems on trees and opposite posets

Abstract

We study transfer systems on partially ordered sets whose Hasse diagrams are rooted trees. We prove there is a bijection between transfer systems on a tree and order-preserving functions to the natural numbers that are bounded by the rank function. We then develop a recurrence for the set of functions and use this to enumerate transfer systems on some families of trees. In addition to our study of trees, we prove for any finite poset $\mathcal{P}$, the lattice of transfer systems on the opposite poset $\mathcal{P}^{op}$ is isomorphic to the opposite lattice of transfer systems on $\mathcal{P}$. We show this by establishing a bijection between weak factorization systems and transfer systems, which builds on the results for lattices shown in previous work of Franchere, Ormsby, Osorno, Qin, and Waugh.