def combine_arguments(args, additional):
    """Combine two dictionaries representing command-line arguments.

    Any duplicate keys will be merged according to the following procedure:
    1. If the value in both dictionaries are lists, the two lists are combined.
    2. Otherwise, the value in the first dictionary is OVERWRITTEN.

    :param args: original command-line arguments
    :type args: dictionary
    :param additional: additional command-line arguments
    :type additional: dictionary

    :return: combined command-line arguments
    :rtype: dictionary
    """
    new_args = args.copy()

    for key, value in additional.items():
        if key in new_args:
            if isinstance(value, list) and isinstance(new_args[key], list):
                new_args[key] += value
            else:
                new_args[key] = value
        else:
            new_args[key] = value

    return new_args