proposition: Lemma mxblockEh B_ : \mxblock_(i, j) B_ i j = \mxrow_j \mxcol_i B_ i j.
proof: Proof. by apply/matrixP => k l; 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)