proposition: Lemma NOABT_head : forall A x y, @no_output_at_backup_trace A (x :: y) -> no_output_at_backup x.
proof: Proof. Proof using. unfold no_output_at_backup_trace, no_output_at_backup. simpl. intuition. Qed.
imports: Verdi(Verdi HandlerMonad)