proposition: Lemma Exists_one_inv : forall P x, Exists P (x::nil) -> P x.
proof: Proof. Proof using. introv H. rewrite* Exists_one_eq in H. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)