proposition: Lemma mx_row_eq : forall m1 m2 n i1 i2 (A1 : 'M_(m1, n)) (A2 : 'M_(m2, n)), mx_row i1 A1 === mx_row i2 A2 -> A1 i1 === A2 i2.
proof: Proof. rewrite/mx_row => m1 m2 n i1 i2 A1 A2 eqA1A2 j. by apply eqA1A2; apply (@Ordinal 1 0). Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms