When I wrote my book, there was a lot of material that I would have liked to have mentioned, but which I had to leave out. After I completed it, new articles and papers also appeared that I would also have mentioned had they been available earlier. Furthermore, I've since come across some older interesting pieces that I didn't find out about in time.
Some of this stuff may be of interest to readers, so I present references to it here.
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Copyright © Richard A. Bartle
17th June, 2003.