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math.CO2026
Protected tails and polynomial-time enumeration of permutations avoiding a direct sum of an increasing pattern and 231
Henning Ulfarsson, Henning Arnór Skeggi Úlfarsson
We give an algorithm counting the permutations that avoid a fixed pattern of the following form: the direct sum of an increasing pattern and 231. The first members of the family ar…
math.CO2026
Inversion monotonicity in subclasses of the 1324-avoiders
Anders Claesson, Svante Linusson, Henning Ulfarsson +1
A collection of patterns is called inversion monotone if , the number of -avoiding permutations of length with inversions, is weakly increasing i…
math.CO2026
A Permutation Avoidance Game with Reverse Replies and Monotone Traps
Henning Ulfarsson
We study the impartial game PAP (``permutations avoiding patterns''), in which players take turns choosing patterns to avoid. We define a set of length patterns, , and sho…