def get_ln_flag_pair_of_bit(flag_bit: int) -> int:
    """Ln Feature flags are assigned in pairs, one even, one odd. See BOLT-09.
    Return the other flag from the pair.
    e.g. 6 -> 7
    e.g. 7 -> 6
    """
    if flag_bit % 2 == 0:
        return flag_bit + 1
    else:
        return flag_bit - 1
Ln Feature flags are assigned in pairs, one even, one odd. See BOLT-09.
    Return the other flag from the pair.
    e.g. 6 -> 7
    e.g. 7 -> 6
    
electrum/lnutil.py