proposition: Lemma map2_xcol j1 j2 : map2_mx (xcol j1 j2 A) (xcol j1 j2 B) = xcol j1 j2 (map2_mx A B).
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)