2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/66650Motivated by work of Stembridge, we study rank functions for Viennot's heaps of pieces. We produce a simple and sufficient criterion for a heap to be a ranked poset and apply the results to the heaps arising from fully commutative words in Coxeter groups.18 pages AMSTeX, 3 figuresCombinatorics06A07text