def successor(self,state):
        action = 0
        if state[0] == 0:
            possible1 =  (state[3], state[1],state[2], state[0],state[4],state[5] ,state[6],state[7], state[8])
            possible2 = (state[1],state[0],state[2], state[3],state[4],state[5], state[6],state[7], state[8])
            next_stage = [(action,possible1), (action,possible2)]
            return next_stage

            ... and the same for each state[x]