proposition: Lemma map2_col' j0 : map2_mx (col' j0 A) (col' j0 B) = col' j0 (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)