proposition: Lemma mult_apart_zero_l x y : x * y ≶ 0 → x ≶ 0.
proof: Proof. intros. apply (strong_extensionality (.* y)). now rewrite mult_0_l. Qed.
imports: Coq.setoid_ring.Ring MathClasses.interfaces.abstract_algebra MathClasses.theory.strong_setoids MathClasses.theory.rings