proposition: Lemma remove_1 : E.eq x y -> ~ In y (remove x m).
proof: Proof. t. Qed.
imports: Coq.PArith.BinPos Coq.PArith.Pnat Coq.Arith.Arith Coq.FSets.FMapInterface Coq.FSets.FMapPositive Fiat.Parsers.ContextFreeGrammar.Carriers Fiat.Common.List.ListFacts Fiat.Common.List.ListMorphisms Fiat.Common.Prod