proposition: Lemma permut_get_4 : forall l1 l2 l3 l4 l5, (l1 \u l2 \u l3 \u l4 \u l5) = (l2 \u l3 \u l4 \u l1 \u l5).
proof: Proof. Proof using. intros. do 2 rewrite (union_assoc l2). apply permut_get_3. Qed.
imports: TLC(LibTactics LibLogic LibReflect LibRelation LibList LibInt LibNat LibOperation LibEpsilon LibSet LibMonoid)