This chapter contains reference material which you should have met before. It is here both to remind you that you have, and to collect it in one place, so you can easily look back and check things when you are in doubt. You are aware by now of just how sequential a subject mathematics is. If you don't understand something when you rst meet it, you usually get a second chance. Indeed you will nd there are a number of ideas here which it is essential you now understand, because you will be using them all the time. So another aim of this chapter is to.
