proposition: Lemma mul_col_perm m n p s (A : 'M_(m, n)) (B : 'M_(n, p)) : col_perm s A *m B = A *m row_perm s^-1 B.
proof: Proof. apply/matrixP=> i k; rewrite !mxE (reindex_perm s^-1). by apply: eq_bigr => j _ /=; rewrite !mxE permKV. 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)