Wilf Equivalences for Patterns in Rooted Labeled Forests

TL;DR

This paper advances the understanding of pattern avoidance in rooted forests by establishing new Wilf equivalences, classifying these equivalences for small patterns, and exploring their properties using combinatorial bijections and cluster methods.

Contribution

It introduces a new family of forest-Wilf equivalences, completes classifications for small patterns, and analyzes the size and nature of these equivalence classes.

Findings

Established a new family of forest-Wilf equivalences.

Classified all forest-Wilf equivalence classes for patterns of length 3 and up to length 5.

Showed that a large fraction of patterns of length n satisfy nontrivial c-forest-Wilf equivalences.

Abstract

Building off recent work of Garg and Peng, we continue the investigation into classical and consecutive pattern avoidance in rooted forests, resolving some of their conjectures and questions and proving generalizations whenever possible. Through extensions of the forest Simion-Schmidt bijection introduced by Anders and Archer, we demonstrate a new family of forest-Wilf equivalences, completing the classification of forest-Wilf equivalence classes for sets consisting of a pattern of length 3 and a pattern of length at most $5$. We also find a new family of nontrivial c-forest-Wilf equivalences between single patterns using the forest analogue of the Goulden-Jackson cluster method, showing that a $(1-o(1))^n$-fraction of patterns of length $n$ satisfy a nontrivial c-forest-Wilf equivalence and that there are c-forest-Wilf equivalence classes of patterns of length $n$ of exponential size. Additionally, we consider a forest analogue of super-strong-c-Wilf equivalence, introduced for permutations by Dwyer and Elizalde, showing that super-strong-c-forest-Wilf equivalences are trivial by enumerating linear extensions of forest cluster posets.