Hi Ronald,
Mendelson' book is an excellent book.
The many editions of Boolos and Jeffrey are very good, but the
mathematical logic part is not really self-contained. I like very much
also the book by Epstein and Carnielli, and Epstein alone wrote nice
big books on both classical and non classical logics, but I do think
that Mendelson is one of the best introduction to classical
mathematical logic. It gives the standard detailed account on
computability, and on Gödel and Löb theorems.
Note that the understanding of UDA does not rely on mathematical
logic, just on the notion of universal machine, and Church thesis
(which I am explaining currently). But the "formal theory" and the
notion of Löbian Machine, relies on mathematical logic. Those matter
are not well known beyond the circle of mathematical logicians.
Gödel's theorem is frequently abused (that does not help).
This makes me think about the book by Torkel Franzèn, which are very
nice. Excellent complement to Mendelson.
Google on "Torkel Franzèn inexhaustibility" and "Torkel Franzèn abuse
Gödel". You can't miss them.
If and when I try to explain AUDA, I can say more. Mendelson does not
introduce to modal logic, but the little book by Bools 1979 does it
very well, before using it for the formal self-reference.
So for AUDA, ma suggestion, for serious studies, is:
1) Mendelson
2) Boolos 1979
Bruno
http://iridia.ulb.ac.be/~marchal/