proposition: Theorem mult_n_1 : forall p : nat, p * 1 = p.
proof: Proof. Admitted. Theorem plus_1_neq_0_firsttry : forall n : nat, (n + 1) =? 0 = false. Proof. intros n. simpl. Abort. Theorem plus_1_neq_0 : forall n : nat, (n + 1) =? 0 = false. Proof. intros n. destruct n as [| n'] eqn:E. - reflexivity. - reflexivity. Qed.