proposition: Lemma mul_col_row m1 m2 n p1 p2 (Au : 'M_(m1, n)) (Ad : 'M_(m2, n)) (Bl : 'M_(n, p1)) (Br : 'M_(n, p2)) : col_mx Au Ad *m row_mx Bl Br = block_mx (Au *m Bl) (Au *m Br) (Ad *m Bl) (Ad *m Br).
proof: Proof. by rewrite mul_col_mx !mul_mx_row. 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)