proposition: Lemma map2_rsubmx : map2_mx (rsubmx Bh) (rsubmx B'h) = rsubmx (map2_mx Bh B'h).
proof: Proof. by apply/matrixP=> i j; 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)