The horror... the horror...
Colonel Curtz, Apocalypse Now
I am indebted to Sina Adineh, Bruce Blackadar, Luciano Salvetti, and Fanxin Wu for pointing out to some mistakes that mysteriously crept into my book while I wasn't looking. The proofs that were included in their entirety were not entirely wrong. Even if there were a few minor changes in a proof, I found it that writing out the complete (and completely correct) proof appeared to be the right way to go. For a pdf file with the errata, click here.