(VAR f x xs y )
(RULES 
        app(app(map,f),nil) -> nil
        app(app(map,f),app(app(cons,x),xs)) -> app(app(cons,app(f,x)),app(app(map,f),xs))
        app(sum,app(app(cons,x),xs)) -> app(app(plus,x),app(sum,xs))
        app(size,app(app(node,x),xs)) -> app(s,app(sum,app(app(map,size),xs)))
        app(app(plus,0),x) -> 0
        app(app(plus,app(s,x)),y) -> app(s,app(app(plus,x),y))
        
)