Posting an article to Usenet produced a fascinating response. In the article (Privatise the Police, on this site under Frontiers of the State) I cited the well-known economist David Friedman. The following day Friedman wrote to me, picking up on another point I made in the same article, and asking if I had found that in his writing or had independently come up with the same thought. As it happens, I had come up with the thought myself - it was not included in the only David Friedman book I have read, as he only thought of it later himself. Our joint idea - that private policing companies would value a reputation among criminals for catching the right person - falls right in the nexus between Friedman's expertise in economics and mine, as an expert on reputation. Do look up the article, by the way. It is one of my favourites.