proposition: Lemma colKl m n1 n2 j1 (A1 : 'M_(m, n1)) (A2 : 'M_(m, n2)) : col (lshift n2 j1) (row_mx A1 A2) = col j1 A1.
proof: Proof. by apply/matrixP=> i j; rewrite !(row_mxEl, 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)