proposition: Lemma seteq_nil_nil' : forall {A} seq, @SetEq A nil seq <-> seq = nil.
proof: Proof. setoid_rewrite SetEq_Symmetric_iff. intro; exact seteq_nil_nil. Qed.
imports: Coq.Setoids.Setoid Coq.Lists.List Coq.Sorting.Permutation Fiat.Common.List.FlattenList Fiat.Common.SetEq