A generating tree with a single label for permutations avoiding the vincular pattern 1-32-4

TL;DR

This paper constructs a generating tree with a single label for permutations avoiding the vincular pattern 1-32-4, clarifying recursive formulas, and providing an algorithm for enumeration and refinement based on right-to-left maxima.

Contribution

It introduces a new generating tree approach for these permutations, explaining recursive formulas and enabling efficient generation and refined counting.

Findings

Provides a generating tree with a single label for the permutations.

Clarifies the recursive formula counting these permutations.

Offers an algorithm to generate and refine enumeration based on a statistic.

Abstract

In this paper we continue the study of permutations avoiding the vincular pattern $1-32-4$ by constructing a generating tree with a single label for these permutations. This construction finally provides a clearer explanation of why a certain recursive formula found by Callan actually counts these permutations, insofar as this formula was originally obtained only as a consequence of a very intricated bijection with a certain class of ordered rooted trees. This responds to a theoretical issue already raised by Duchi, Guerrini and Rinaldi. As a byproduct, we also obtain an algorithm to generate all these permutations and we refine their enumeration according to a simple statistic, which is the number of right-to-left maxima to the right of 1.