fact: Definition is_tree (g : Gph) (x : V) : Prop := forall y, reachable g x y -> exists !(p : path), g |= p is x ~o~> y satisfying (fun _ => True).
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