(VAR k l x y z )
(RULES 
        minus(x, 0) -> x
        minus(s(x), s(y)) -> minus(x, y)
        quot(0, s(y)) -> 0
        quot(s(x), s(y)) -> s(quot(minus(x, y), s(y)))
        plus(0, y) -> y
        plus(s(x), y) -> s(plus(x, y))
        minus(minus(x, y), z) -> minus(x, plus(y, z))
        app(nil, k) -> k
        app(l, nil) -> l
        app(cons(x, l), k) -> cons(x, app(l, k))
        sum(cons(x, nil)) -> cons(x, nil)
        sum(cons(x, cons(y, l))) -> sum(cons(plus(x, y), l))
        sum(app(l, cons(x, cons(y, k)))) -> sum(app(l, sum(cons(x, cons(y, k)))))
        
)