proposition: Lemma in_single_inv : forall x y : A, x \in (\{y}:multiset A) -> x = y.
proof: Proof. Proof using. intros. rewrite @in_single_eq in H. auto. typeclass. Qed.
imports: TLC(LibTactics LibLogic LibReflect LibRelation LibList LibInt LibNat LibOperation LibEpsilon LibSet LibMonoid)