**Introduction.**

This is the first of what I hope will be a long series of posts aimed at providing back-up to first-year Cambridge mathematicians. This may seem a strange thing to do, since the Cambridge system of supervisions (classes taught on a one-to-two basis, usually discussing questions set by lecturers) already provides an excellent back-up to lectures. Do Cambridge undergraduates, who already have closer attention than in any other university I know about, really need even more help?

Well, perhaps they are lucky enough to need it less than mathematicians anywhere else, but there are several facts that convince me that even more can be done than is done already. Let me list a few of them.

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