(VAR m n x y )
(RULES 
        le(0, y) -> true
        le(s(x), 0) -> false
        le(s(x), s(y)) -> le(x, y)
        app(nil, y) -> y
        app(add(n, x), y) -> add(n, app(x, y))
        low(n, nil) -> nil
        low(n, add(m, x)) -> if_low(le(m, n), n, add(m, x))
        if_low(true, n, add(m, x)) -> add(m, low(n, x))
        if_low(false, n, add(m, x)) -> low(n, x)
        high(n, nil) -> nil
        high(n, add(m, x)) -> if_high(le(m, n), n, add(m, x))
        if_high(true, n, add(m, x)) -> high(n, x)
        if_high(false, n, add(m, x)) -> add(m, high(n, x))
        head(add(n, x)) -> n
        tail(add(n, x)) -> x
        isempty(nil) -> true
        isempty(add(n, x)) -> false
        quicksort(x) -> if_qs(isempty(x), low(head(x), tail(x)), head(x), high(head(x), tail(x)))
        if_qs(true, x, n, y) -> nil
        if_qs(false, x, n, y) -> app(quicksort(x), add(n, quicksort(y)))
        
)