I'm in the middle of revising my freely available and much-downloaded introductory notes Gödel Without (Too Many) Tears. (They are a sort of cut down version of part of my Gödel book, and I'm updating the notes to fit better with the second edition of the book, although they are intended to be stand-alone).
I'd rather like to add to the end of each chunk of the notes a very short section of "Further/Parallel Reading", where this ideally points to again to freely available material -- webpages or pdfs which are at a similar sort of introductory level (and very clear, and relatively short).
I'd be really grateful, then, to learn about any free resources out there (other than Wikipedia!) that you have found particularly useful as a student or teacher, on any of the following topics from the first half of the notes:
- The very idea of a diagonal argument
- Robinson Arithmetic
- Induction
- (First-order) Peano Arithmetic
- The beginnings of the arithmetical hierarchy/quantifier complexity
- Primitive recursive functions
- Why the p.r. functions can be expressed in the language of basic arithmetic/ represented in Robinson Arithmetic.
(I hope no one thinks this is an inappropriate use of this wonderful resource to ask this here! But others might be interested in the answers, even if they never get round to my notes, and as I say, the notes themselves are freely provided, so any improvements should help students everywhere.)
