def list_substract(list1, list2):
    """OK [52]
    Returns list1 where each element is substracted by the corresponding
    list2 element. Returns None if the lenght of the lists is not the same.
    """
    if not list1:
        return None
    result_list = []
    if len(list1) != len(list2):
        #print("list substract with lists of different length!!, abort")
        return None
    for count, value in enumerate(list1):
        result_list.append(value - list2[count])
    return result_list