proposition: Lemma mxvec_cast : #|{:'I_m * 'I_n}| = (m * n)%N.
proof: Proof. by rewrite card_prod !card_ord. 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)