can't get org-mode noweb tangle to work

["Charles R (Charlie) Martin" <chasrmartin@gmail.com>]

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I'm trying to get literate programming with `:noweb` syntax working in
org-mode. I think I'm down to about the minimum case:

        #+TITLE: Console Tic Tac Toe
    #+SUBTITLE: A Literate Program in EMACS Org-Mode
    #+AUTHOR: Charlie Martin
    #+STARTUP: showall

    #+BEGIN_SRC python :tangle yes :noweb
      import sys
      import os

      def main(args):
          <<initialize-the-game-board>>

      if __name__ == "__main__":
          main(sys.argv)
    #+END_SRC

    #+NAME: initialize-the-game-board
    #+BEGIN_SRC python :tangle yes :noweb
      board = [[-1 for x in range(3)] for y in range(3)]
    #+END_SRC

but when I tangle it I get:

    import sys
    import os

    def main(args):
        <<initialize-the-game-board>>

    if __name__ == "__main__":
        main(sys.argv)

    board = [[-1 for x in range(3)] for y in range(3)]

I've tried permuting the argument, flags, and so on to no avail.

EMACS version is 25.3.1 MacOS, org-mode 9.1.3

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