(VAR f x xs ys )
(RULES 
        app(app(append,nil),ys) -> ys
        app(app(append,app(app(cons,x),xs)),ys) -> app(app(cons,x),app(app(append,xs),ys))
        app(app(flatwith,f),app(leaf,x)) -> app(app(cons,app(f,x)),nil)
        app(app(flatwith,f),app(node,xs)) -> app(app(flatwithsub,f),xs)
        app(app(flatwithsub,f),nil) -> nil
        app(app(flatwithsub,f),app(app(cons,x),xs)) -> app(app(append,app(app(flatwith,f),x)),app(app(flatwithsub,f),xs))
        
)