proposition: Lemma set_cons (a : T) s : [set y in a :: s] = a |: [set y in s].
proof: Proof. by apply/setP => y; rewrite !inE. Qed.
imports: mathcomp(all_ssreflect ssralg fingroup zmodp poly ssrnum) mathcomp(matrix perm) ssr_ext ssralg_ext fdist