proposition: Lemma mult_eq_0 : forall n m, n * m = 0 -> n = 0 \/ m = 0.
proof: Proof. Admitted. Theorem or_commut : forall P Q : Prop, P \/ Q -> Q \/ P. Proof. Admitted. Module MyNot. Definition not (P:Prop) := P -> False. Notation "~ x" := (not x) : type_scope. Check not. End MyNot. Theorem ex_falso_quodlibet : forall (P:Prop), False -> P. Proof. intros P contra. destruct contra. Qed.
imports: Tactics