docs: def links_between(a, b, machine):
      """Get the set of working links connecting chips a and b.
  
      Parameters
      ----------
      a : (x, y)
      b : (x, y)
      machine : :py:class:`~rig.place_and_route.Machine`
  
      Returns
      -------
      set([:py:class:`~rig.links.Links`, ...])
      """
      ax, ay = a
      bx, by = b
      return set(link for link, (dx, dy) in ((l, l.to_vector()) for l in Links)
                 if (ax + dx) % machine.width == bx and
                 (ay + dy) % machine.height == by and
                 (ax, ay, link) in machine)