Permutations Avoiding Bipartite Partially Ordered Patterns Have a Regular Insertion Encoding
Christian Bean, Émile Nadeau, Jay Pantone, Henning Úlfarsson · The Electronic Journal of Combinatorics · 2024
We prove that any class of permutations defined by avoiding a partially ordered pattern (POP) with height at most two has a regular insertion encoding and thus has a rational generating function. Then, we use Combinatorial Exploration to find combinatorial specifications and generating functions for hundreds of other permutation classes defined by avoiding a size 5 POP, allowing us to resolve several conjectures of Gao and Kitaev (2019) and of Chen and Lin (2024).