def Bern_to_Fierz_nunu(C,ddll):
    """From semileptonic Bern basis to Fierz semileptonic basis for Class V.
    C should be the corresponding leptonic Fierz basis and
    `ddll` should be of the form 'sbl_enu_tau', 'dbl_munu_e' etc."""
    ind = ddll.replace('l_','').replace('nu_','')
    return {
            'F' + ind + 'nu': C['nu1' + ind],
            'F' + ind + 'nup': C['nu1p' + ind],
            }