proposition: Lemma submxblockEh A i j : submxblock A i j = submxcol (submxrow A j) i.
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)