proposition: Lemma pfoot_ptail: forall (g : Gph) l f, pfoot g l = f -> pfoot g (ptail g l) = f.
proof: Proof. intros. destruct l. destruct l; auto. rewrite pfoot_cons in H. apply H. Qed.
imports: Coq.Logic.ProofIrrelevance Coq.micromega.Lia CertiGraph.lib.Coqlib CertiGraph.lib.EnumEnsembles CertiGraph.lib.List_ext CertiGraph.lib.EquivDec_ext CertiGraph.graph.graph_model Coq.Lists.List Coq.Lists.ListDec