fact: Variables (P : tree -> Prop) (Q : list tree -> Prop) (P1 : forall n, P (leaf n)) (P2 : forall l, Q l -> P (node l)) (Q1 : Q nil) (Q2 : forall t l, P t -> Q l -> Q (t::l)).
imports: TLC(LibTactics LibLogic LibReflect LibFun LibEpsilon LibList LibInt LibNat LibProd LibSum LibRelation LibWf LibFix LibStream) ZifyNat