proposition: Lemma rowKd m1 m2 n i2 (A1 : 'M_(m1, n)) (A2 : 'M_(m2, n)) : row (rshift m1 i2) (col_mx A1 A2) = row i2 A2.
proof: Proof. by apply/matrixP=> i j; rewrite !(col_mxEd, 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)