sigma - Restricted Growth Functions and p, q-Stirling Numbers

Abstract The restricted growth functions are known to encode set partitions. They are words whose subword of leftmost occurrences is the identity permutation. We generalize the notion of restricted growth function by considering words whose subword of leftmost occurrences is a fixed general permutation. We prove a natural generalization of results of Wachs and White which state that the enumerators for the joint distribution of two pairs of inversion like statistics on restricted growth functions are the p, q-Stirling numbers.