As I’ve said, I’m in the middle of revising my much-downloaded introductory notes Gödel Without (Too Many) Tears. 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 — i.e. webpages or pdfs which are at a similar sort of introductory level (and very clear, and relatively short).

I’d love to hear, then, 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.

Pointers to other people’s lecture handouts and all other suggestions most gratefully received!

MarkStephen Simpson’s home page http://www.personal.psu.edu/t20/ contains very interesting resources on these topics, especially his lecture notes on FOM.

Mozibur UllahI found Yanofskys discussion of the diagonal argument taken from a paper by Lawvere where he discusses it in a categorical context interesting and readable.