fact: Fixpoint xfold (m : t) (v : B) (i : elt) := match m with | Leaf => v | Node l true r => xfold r (f (rev i) (xfold l v i~0)) i~1 | Node l false r => xfold r (xfold l v i~0) i~1 end.
imports: Bool PeanoNat BinPos OrderedType OrderedTypeEx FSetInterface