def nice_true_ces(tc):
    """Format a true |CauseEffectStructure|."""
    cause_list = []
    next_list = []
    cause = '<--'
    effect = '-->'
    for event in tc:
        if event.direction == Direction.CAUSE:
            cause_list.append(["{0:.4f}".format(round(event.alpha, 4)),
                               event.mechanism, cause, event.purview])
        elif event.direction == Direction.EFFECT:
            next_list.append(["{0:.4f}".format(round(event.alpha, 4)),
                              event.mechanism, effect, event.purview])
        else:
            validate.direction(event.direction)

    true_list = [(cause_list[event], next_list[event])
                 for event in range(len(cause_list))]
    return true_list
Format a true |CauseEffectStructure|.