proposition: Lemma row_thin_mx m n (A : 'M_(m,0)) (B : 'M_(m,n)) : row_mx A B = B.
proof: Proof. apply/matrixP=> i j; rewrite mxE; case: splitP=> [|k H]; first by case. by congr fun_of_matrix; exact: val_inj. 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)