def phase_active(gene):
    """
    Determine if a phase is active.
    :param gene: list, gene describing a phase.
    :return: bool, true if active.
    """
    # The residual bit is not relevant in if a phase is active, so we ignore it, i.e. gene[:-1].
    return sum([sum(t) for t in gene[:-1]]) != 0