'Return the state of the new machine corresponding to the
set of old machine states represented by |state_set|. A new
state will be created if necessary. If any of the old states
are accepting states, the new state will be an accepting state
with the highest priority action from the old states.'

def old_to_new(self, old_state_set):

    key = self.make_key(old_state_set)
    new_state = self.old_to_new_dict.get(key, None)
    if (not new_state):
        action = self.highest_priority_action(old_state_set)
        new_state = self.new_machine.new_state(action)
        self.old_to_new_dict[key] = new_state
        self.new_to_old_dict[id(new_state)] = old_state_set
    return new_state
