proposition: Lemma ex_not_not_all2 : forall P : U -> Prop, (exists n : U, P n) -> ~ (forall n : U, ~ P n).
proof: Proof. unfold not in |- *; intros P exnot allP. elim exnot; auto. Qed.
imports: List DistributedReferenceCounting.machine2.invariant8