Permutation class

Summary

In the study of permutations and permutation patterns, a permutation class is a set $C$ of permutations for which every pattern within a permutation in $C$ is also in $C$. In other words, a permutation class is a hereditary property of permutations, or a downset in the permutation pattern order. A permutation class may also be known as a pattern class, closed class, or simply class of permutations.