Yes. I'm afraid I'm heading off and can't think of a good way to hint Right Now. (It's Exercise 4.13 in http://www.inference.phy.cam.ac.uk/mackay/itila/book.ht

Yes. I'm afraid I'm heading off and can't think of a good way to hint Right Now. (It's Exercise 4.13 in http://www.inference.phy.cam.ac.uk/mackay/itila/book.html http://www.inference.phy.cam.ac.uk/mackay/itila/book.html ... and there is a solution and other related weighing problems in there.)