code: def _second(self):
          
  
          self._second_one_loop()
          A = self._A
          if A[2, 1] == 0:
              return True
          elif A[2, 1] % A[1, 1] == 0:
              self._second_finalize()
              self._Ps += self._L
              self._L = []
              return True
          else:
              return False
docs: Find Smith normal form for Right-low 2x2 matrix