define forward_difference(l);
    lvars res = [], prev, el;
    if l = [] then
        return([]);
    endif;
    front(l) -> prev;
    for el in back(l) do
        cons(el - prev, res) -> res;
        el -> prev;
    endfor;
    rev(res);
enddefine;

define nth_difference(l, n);
    lvars res = l, i;
    for i from 1 to n do
        forward_difference(res) -> res;
    endfor;
    res;
enddefine;