fact: Definition well_defined_list (pg: PreGraph V E) {ma: MathGraph pg is_null} (l : list V) := forall x, In x l -> weak_valid pg x.
imports: CertiGraph.lib.Coqlib CertiGraph.lib.Ensembles_ext CertiGraph.lib.EquivDec_ext CertiGraph.lib.List_ext CertiGraph.lib.relation_list CertiGraph.lib.Equivalence_ext CertiGraph.graph.graph_model CertiGraph.graph.graph_gen