proposition: Lemma submxcol_mul n' m (B : 'M[R]_(sp, n')) (A : 'M[R]_(n', m)) i : submxcol B i *m A = submxcol (B *m A) i.
proof: Proof. by apply/matrixP=> j s; rewrite !mxE; under eq_bigr do rewrite !mxE. 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)