proposition: Lemma ngr_firstn_gen_clear: forall g1 g2 gen to, graph_has_gen g1 to -> firstn_gen_clear g1 to -> new_gen_relation gen g1 g2 -> firstn_gen_clear g2 to.
proof: Proof. intros. red in H1. destruct (graph_has_gen_dec g1 gen). - subst; auto. - destruct H1 as [gen_i [? ?]]. subst g2. rewrite <- (Nat2Z.id to) in *. apply firstn_gen_clear_add; auto. Qed.
imports: Coq.ZArith.ZArith Coq.Program.Basics compcert.lib.Integers compcert.common.Values VST.veric.base VST.veric.Clight_lemmas VST.veric.val_lemmas VST.veric.shares VST.msl.seplog VST.msl.shares VST.zlist.sublist VST.floyd.coqlib3 VST.floyd.functional_base VST.floyd.data_at_rec_lemmas CertiGraph.lib.Coqlib CertiGraph.lib.EquivDec_ext CertiGraph.lib.List_ext CertiGraph.graph.graph_model CertiGraph.graph.graph_gen CertiGraph.graph.path_lemmas CertiGraph.graph.subgraph2 CertiGraph.graph.graph_relation CertiGraph.graph.graph_isomorphism CertiGraph.graph.reachable_ind CertiGraph.CertiGC.GCGraph