fact: Axiom app_eq_one : ys ++ zs = one x ++ xs -> (exists qs, ys = x :: qs /\ xs = qs ++ zs) \/ (ys = nil /\ zs = x :: xs).
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.AssocList Metalib.MetatheoryAtom Metalib.LibTactics