Squashed commit of the following:

commit db2ec8743958b55b18e29a02b1fc342170c39024
Author: Oliver Chick <oliver.chick--dtg-git@cl.cam.ac.uk>
Date:   Wed Apr 3 16:48:28 2013 +0100

    Backward working

commit c21735d79aea94da06e141e8ba38d887ba16c82e
Author: Oliver Chick <oliver.chick--dtg-git@cl.cam.ac.uk>
Date:   Wed Apr 3 16:46:14 2013 +0100

    Forward working