code: def has_cell(self, s):
          
  
          for t in self.transitions:
              if len(t.lhs[s]) != 1:
                  return False
              if len(t.rhs[s]) != 1:
                  return False
              if t.lhs[s].position != 0:
                  return False
              if t.rhs[s].position != 0:
                  return False
          return True
docs: Tests whether store `s` is a cell, that is, it uses exactly one
          cell, and there can take on only a finite number of states).