docs: def extract_channel(k, cdim):
      """Create a :class:`CPermutation` that extracts channel `k`
  
      Return a permutation circuit that maps the k-th (zero-based)
      input to the last output, while preserving the relative order of all other
      channels.
  
      Args:
          k (int): Extracted channel index
          cdim (int): The circuit dimension (number of channels)
  
      Returns:
          Circuit: Permutation circuit
      """
      n = cdim
      perm = tuple(list(range(k)) + [n - 1] + list(range(k, n - 1)))
      return CPermutation.create(perm)