Preface xiii Mitsunori Ogihara(University of Rochester),R.W.Robinson(University of Georgia). Yaakov L.Varol (University of Nevada,Reno),William W.White(Southern Illinois Uni- versity at Edwardsville),Dawn Wilkins(University of Mississippi),and Abdou Youssef (George Washington University). We thank our editors at Addison-Wesley,Maite Suarez-Rivas and Karen Wernholm, for their confidence and patience in working with us on this projcct that often dcparted from standard production procedures and schedules.We thank Joan Flaherty for her painstak- ingly careful copy editing and valuable suggestions for improving the presentation.Brooke Albright's careful proofreading detected many errors that had survived earlier scrutiny;of course,any that remain are the fault of the authors. We thank Keith Mayers for assisting us in various ways.Sara thanks him for not reminding her too often that she broke her wedding vow to work less than seven days a week. Sara Baase,San Diego,California http://www-rohan.sdsu.edu/faculty/baase Allen Van Gelder,Santa Cruz,Califoria http://www.cse.ucsc.edu/personnel/faculty/avg.html June,1999