The original idea for writing this monograph arose from conversations between Ben Noble and the late Julian Wu. We are indebted to Ben Noble for many valuable exchanges regarding the scope and historical details included in this book. Among the other surviving key members of the
Mathematics Research Center, we are particularly grateful to Carl de Boor, Michael Crandall, and Olvi Mangasarian for their insightful comments and input. We are also much indebted to Annetta Hamilton Rosser for her help in many respects, including her comments on drafts.