def get_orbit_variables(accel: str):
    """ Get the variable names used for orbit setup.
    Args:
        accel (str): 'lhc' or 'hllhc'

    Returns:
        tuple of 0: list of all orbit variables, apart form those in 1
                 1: dictionary of additional variables, that in the
                    default configurations have the same value as another variable

    """
    if accel == "hllhc":
        on_variables = (
            'crab1', 'crab5',  # exists only in HL-LHC
            'x1', 'sep1', 'o1', 'a1',
            'x2', 'sep2', 'o2', 'a2',
            'x5', 'sep5', 'o5', 'a5',
            'x8', 'sep8', 'o8', 'a8',
            'alice', 'sol_alice', 'lhcb', 'sol_atlas', 'sol_cms',
        )
        special = {}
    else:
        on_variables = (
            'x1', 'sep1', 'o1', 'oh1', 'ov1',
            'x2', 'sep2', 'o2', 'oe2', 'a2', 'oh2', 'ov2',
            'x5', 'sep5', 'o5', 'oh5', 'ov5',
            'x8', 'sep8', 'o8', 'a8', 'sep8h', 'x8v', 'oh8', 'ov8',
            'alice', 'sol_alice', 'lhcb', 'sol_atlas', 'sol_cms',
        )
        special = {'on_ssep1': 'on_sep1', 'on_xx1': 'on_x1',
                   'on_ssep5': 'on_sep5', 'on_xx5': 'on_x5',
                   }
    variables = [f'on_{var}' for var in on_variables] + [f'phi_ir{ir:d}' for ir in (1, 2, 5, 8)]
    return variables, special