fact: Fixpoint forest_head (tl: list Tree) : list Vertex := match tl with | nil => nil | EPT :: tl' => forest_head tl' | T v l :: tl' => v :: forest_head tl' end.
imports: Coq.Arith.Arith CertiGraph.lib.Coqlib CertiGraph.lib.EnumEnsembles CertiGraph.lib.EquivDec_ext CertiGraph.lib.List_ext CertiGraph.graph.graph_model CertiGraph.graph.path_lemmas CertiGraph.graph.subgraph2 CertiGraph.graph.MathGraph CertiGraph.graph.FiniteGraph CertiGraph.graph.reachable_computable Coq.Lists.List