ABSTRACT
This chapter is written more or less independently of the rest of the text, so that it can be read at any time during the course, including at the beginning if you wish. Some topics discussed in other parts of the text are briefl y repeated here to make the present chapter self-contained (or for review, if you have already read most of the text). References are made to specifi c sections of the book for more detail on some of the concepts discussed.
