I am looking for literature that is as self-explanatory, easy, gentle, readable to the beginner, suitable for self-study, etc.. as possible, in the following fields. (I mean the mathematical part as well as the philosophical)
constructive mathematics
reverse mathematics
foundations (frameworks, formal systems, basic ideas/concepts) of mathematics
I have a few years of professional training in 'mainstream' mathematics, but its been some years since then. I've done an introduction to logic and looked a bit into proof theory.
I would be interested in your suggestions as well as (also brief) explanations why you favor that particular work.
Thanks in advance,
Ettore