fact: Definition node_pred_dec (P: NodePred) (x: Vertex): {P x} + {~ P x} := projT2 P x.
imports: Coq.Logic.ProofIrrelevance CertiGraph.lib.Ensembles_ext CertiGraph.lib.EquivDec_ext CertiGraph.lib.List_ext CertiGraph.lib.relation_list CertiGraph.lib.Equivalence_ext