On the Alternating runs polynomial in type B and D Coxeter Groups

Abstract

Wilf showed that the the alternating runs polynomial $R_n(t)$ counting the number of permutations in the Symmetric group is divisible by $(1+t)^m$ where $m = \lfloor (n-2)/2 \rfloor$. Recently, B\'{o}na gave a group action based proof. Type B and D analogues of Wilf's result are known. In this note, we extend B\'{o}na's proof to prove the type B and D analogue.