proposition: Lemma map2_col j : map2_mx (col j A) (col j B) = col j (map2_mx A B).
proof: Proof. by apply/colP=> i; 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)