Which four unit textbook would you recommend?
Tbh, seeing as though you're from a selective school, you should consider Terry Lee's textbook. It's in depth level of difficulty and its rigour is mostly targeted for selective school students.
Oh really? The limited experience I've had with it (not being a 4U student), I liked it. Probably because I wasn't using it for practice questions so much as explanation of concepts
If you're looking for a good set of 4U notes, these are worth a look
I saw it ok for setting the grounds, But that was about it.
I find it more like maths in focus if anything, except unlike MAF the 4u Cambridge book still offers difficulty.
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Regarding (new) Fitzpatrick: Pretty good but sometimes goes into irrelevant information that can be confusing. Quite well set out and has worked solutions to many problems though.