http://www.cus.cam.ac.uk/~fanf2/hermes/doc/talks/2005-02-eximconf/paper.pdf
http://www.cus.cam.ac.uk/~fanf2/hermes/doc/talks/2005-02-ukuug/paper.pdf
http://www.cus.cam.ac.uk/~fanf2/hermes/doc/talks/2005-02-eximconf/paper.pdf
http://www.cus.cam.ac.uk/~fanf2/hermes/doc/talks/2005-02-ukuug/paper.pdf