This book is intended for mathematicians. Its origins lie in a course of lectures given by an algebraist to a class which had just completed a sub- stantial course on abstract algebra. Consequently, our treatment ofthe sub- ject is algebraic. Although we assurne a reasonable level of sophistication in algebra, the text requires little more than the basic notions of group, ring, module, etc. A more detailed knowledge of algebra is required for some of . the exercises. We also assurne a familiarity with the main ideas of set theory, including cardinal numbers and Zorn's Lemma. In this book, we...