proposition: Lemma perm_mx_is_perm n (s : 'S_n) : is_perm_mx (perm_mx s).
proof: Proof. by apply/is_perm_mxP; exists s. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)