code: def go(self, state, direction):
          "Return the state that results from going in this direction."
          state1 = vector_add(state, direction)
          return if_(state1 in self.states, state1, statef go(self, state, direction):
          "Return the state that results from going in this direction."
          state1 = vector_add(state, direction)
          return if_(state1 in self.states, state1, state)
docs: Return the state that results from going in this direction.