Enumeration of fixed points of an involution on $\beta (1,0)$-trees

Abstract

$\beta (1,0)$-trees provide a convenient description of rooted non-separable planar maps. The involution $h$ on $\beta (1,0)$-trees was introduced to prove a complicated equidistribution result on a class of pattern-avoiding permutations. In this paper, we describe and enumerate fixed points of the involution $h$. Intriguingly, the fixed points are equinumerous with the fixed points under taking the dual map on rooted non-separable planar maps, even though the fixed points do not go to each other under the know (natural) bijection between the trees and the maps.