code: def is_in_list(self, plane_list):
          
          for plane in plane_list:
              if self.is_same_plane_as(plane):
                  return True
          return False
docs: Checks whether the plane is identical to one of the Planes in the plane_list list of Planes
          :param plane_list: List of Planes to be compared to
          :return: True if the plane is in the list, False otherwise