docs: def calculate_iI_correspondence(omega):
      r"""Get the correspondance between degenerate and nondegenerate schemes."""
      Ne = len(omega[0])
      om = omega[0][0]
      correspondence = []
      I = 0
      for i in range(Ne):
          if omega[i][0] != om:
              om = omega[i][0]
              I += 1
          correspondence += [(i+1, I+1)]
      Nnd = I+1
  
      def I_nd(i):
          return correspondence[i-1][1]
  
      def i_d(I):
          for i in range(Ne):
              if correspondence[i][1] == I:
                  return correspondence[i][0]
  
      return i_d, I_nd, Nnd