proposition: Lemma length_one_inv : forall l, length l = 1 -> exists x, l = x::nil.
proof: Proof. Proof using. introv N. destruct l as [|x [|]]; rew_list in *; tryfalse. eauto. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)