proposition: Lemma in_union_get_3 : forall x l1 l2 l3 l4, x \in l3 -> x \in (l1 \u l2 \u l3 \u l4).
proof: Proof. Proof using. intros. apply in_union_r. apply~ in_union_get_2. Qed.
imports: TLC(LibTactics LibLogic LibReflect LibRelation LibList LibInt LibNat LibOperation LibEpsilon LibSet LibMonoid)