descents w
A permutation $p=(p_1 \, \dots \, p_n)$ has a descent at $i$ (for $i < n$) if $p(i) > p(i+1)$.
i1 : p = permutation {3,1,2,5,4} o1 = Permutation{3, 1, 2, 5, 4} o1 : Permutation
i2 : descents p o2 = {1, 4} o2 : List
The object descents is a method function.