A bijection between the irreducible k-shapes and the surjective pistols of height k-1

This paper constructs a bijection between irreducible $k$-shapes and surjective pistols of height $k-1$, which carries the “free $k$-sites” to the fixed points of surjective pistols. The bijection confirms a conjecture of Hivert and Mallet (FPSAC 2011) that the number of irreducible $k$-shape is counted by the Genocchi number $G_{2k}$.