def get_model_to_author_dict(model_name_tuples, lower=True):
    """
    Get a dictionary of model names mapped to author names.

    Args:
        model_name_tuples (list or set): An iterable of ModelNames tuples of
            (model_name, author_name). Each name will be lower-case only.
        lower (bool, optional): Make all output names lower-case.
            Defaults to True.

    Returns:
        dict: Dictionary mapping model names to author names. Output will only
            be in lower-case.
    """
    output = {}

    for (model_name, author_name) in model_name_tuples:
        if lower:
            model_name = model_name.lower()
            author_name = author_name.lower()

        if model_name in output:
            output[model_name].append(author_name)
        else:
            output[model_name] = [author_name]

    return output