def find_missing(integers_list, start=None, limit=None):
    """ Given a list of integers and optionally a start and an end
        finds all integers from start to end that are not in the list
    """
    start = start if start is not None else integers_list[0]
    limit = limit if limit is not None else integers_list[-1]
    return [i for i in range(start, limit + 1) if i not in integers_list]