def model_variables(price_model, hlcm, elcm, wah_lcm, developer_access_cols):
    """
    Returns a set of the columns/variables used by various models.

    """
    return set().union(*[
        price_model.columns_used(),
        hlcm.columns_used(),
        elcm.columns_used(),
        wah_lcm.columns_used(),
        developer_access_cols
    ])