proposition: Lemma NOABT_singleton_inl : forall A h r, @no_output_at_backup_trace A [(h, inl r)].
proof: Proof. Proof using. unfold no_output_at_backup_trace, no_output_at_backup. simpl. intuition. subst. simpl in *. discriminate. Qed.
imports: Verdi(Verdi HandlerMonad)