Skew Dyck paths

In this paper we study the class S of skew Dyck paths, i.e. of those lattice paths that are in the first quadrant, begin at the origin, end on the x-axis, consist of up steps U = ( 1 , 1 ) , down steps D = ( 1 , - 1 ) , and left steps L = ( − 1 , - 1 ) , and such that up steps never overlap with left steps. In particular, we show that these paths are equinumerous with several other combinatorial objects, we describe some involutions on this class, and finally we consider several statistics on S .