(VAR f h t x )
(RULES 
        app(app(twice,f),x) -> app(f,app(f,x))
        app(app(map,f),nil) -> nil
        app(app(map,f),app(app(cons,h),t)) -> app(app(cons,app(f,h)),app(app(map,f),t))
        app(app(fmap,nil),x) -> nil
        app(app(fmap,app(app(cons,f),t_f)),x) -> app(app(cons,app(f,x)),app(app(fmap,t_f),x))
        
)