docs: def iter_links(self):
          """An iterator over the working links in the machine.
  
          Generates a series of (x, y, link) tuples.
          """
          for x in range(self.width):
              for y in range(self.height):
                  for link in Links:
                      if (x, y, link) in self:
                          yield (x, y, link)