proposition: Lemma map_in_iff {elt elt'} m x (f : elt -> elt') : In x (map f m) <-> In x m.
proof: Proof. rewrite !in_find, map_find. apply option_map_some. Qed.
imports: Coq(Bool Equalities Orders OrdersFacts OrdersLists) Coq(Morphisms Permutation SetoidPermutation) MMaps(Utils Comparisons Interface)