proposition: Lemma submxcol_matrix B_ i : submxcol (\mxblock_(i, j) B_ i j) i = \mxrow_j B_ i j.
proof: Proof. by rewrite mxblockEv mxcolK. 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)