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)