rem: return lPtr;
add: return NULL;
context: Ns_ListCopy(Ns_List *lPtr){    Ns_List *curPtr, *newPtr, *headPtr;    if (lPtr == NULL) {        return lPtr;    }    headPtr = curPtr = Ns_ListCons(lPtr->first, NULL);    for (lPtr = lPtr->rest; lPtr != NULL; lPtr = lPtr->rest) {        newPtr = Ns_ListCons(lPtr->first, NULL);        curPtr->rest = newPtr;        curPtr = newPtr;    }    newPtr->rest = NULL;        return headPtr;}