(VAR f x xs y )
(RULES 
        app(app(ack,0),y) -> app(succ,y)
        app(app(ack,app(succ,x)),y) -> app(app(ack,x),app(succ,0))
        app(app(ack,app(succ,x)),app(succ,y)) -> app(app(ack,x),app(app(ack,app(succ,x)),y))
        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(app(filter,f),nil) -> nil
        app(app(filter,f),app(app(cons,x),xs)) -> app(app(app(app(filter2,app(f,x)),f),x),xs)
        app(app(app(app(filter2,true),f),x),xs) -> app(app(cons,x),app(app(filter,f),xs))
        app(app(app(app(filter2,false),f),x),xs) -> app(app(filter,f),xs)
        
)