proposition: Lemma submxblockD (B B' : 'M[V]_(sp, sq)) i j : submxblock (B + B') i j = submxblock B i j + submxblock 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)