A number of people took part in the making of this work. Mark Hubbard edited every version of every chapter over its seven years of development. His help was critically important. Tom Stachnik and James Henning listened, encouraged, and supported me during times of need. The tables and figures were given final form by Ward Barnett Computer Services in Minneapolis. The people at Praeger believed in the work and gave it final form. My thanks goes to all of them.