(VAR f h l t x )
(RULES 
        app(app(app(fold,f),nil),x) -> x
        app(app(app(fold,f),app(app(cons,h),t)),x) -> app(app(app(fold,f),t),app(app(f,x),h))
        app(sum,l) -> app(app(app(fold,add),l),0)
        app(app(app(fold,mul),l),1) -> app(prod,l)
        
)