proposition: Lemma mul_delta_mx_0 m n p (j1 j2 : 'I_n) (i1 : 'I_m) (k2 : 'I_p) : j1 != j2 -> delta_mx i1 j1 *m delta_mx j2 k2 = 0.
proof: Proof. by rewrite mul_delta_mx_cond => /negPf->. 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)