proposition: Lemma empty_1 : Empty (empty elt).
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