proposition: Lemma in_filterP_iff A (x : A) f l : In x (filterP f l) <-> In x l /\ f x.
proof: Proof. induction l; ins; desf; ins; try (rewrite IHn; clear IHn); intuition; desf; eauto. Qed.
imports: HahnBase HahnSets Arith Lia Setoid Morphisms Sorted IndefiniteDescription List Permutation