code: def _set_zero(self, i, j, a, b, r, s, t):
          
  
          L = np.eye(3, dtype='intc')
          L[i, i] = s
          L[i, j] = t
          L[j, i] = -b // r
          L[j, j] = a // r
          self._L.append(L.copy())
          self._A = np.dot(L, self._A)
docs: Let A[i, j] be zero based on Bezout's identity
  
             [ii ij]
             [ji jj] is a (k,k) minor of original 3x3 matrix.