input: def substring_in_order(string: str) -> List[str]:
      """ Generate a list of all substrings of a given string in order from longest to shortest length.
      >>> substring_in_order("abc")
      ['abc', 'ab', 'bc', 'a', 'b', 'c']
      >>> substring_in_order("abcd")
      ['abcd', 'abc', 'bcd', 'ab', 'bc', 'cd', 'a', 'b', 'c', 'd']
      """
output:     substrings = []
      n = len(string)
      for length in range(n, 0, -1):
          for start in range(n - length + 1):
              substrings.append(string[start:start + length])
      return substrings