# Mendelson's *Mathematical Logic* and the missing Appendix on the consistency of PA

A very soft question, but I hope not out of order here.

In the first edition of Elliott Mendelson's classic Introduction to Mathematical Logic (1964) there is an appendix, giving a version of Schütte's (1951) variation on Gentzen's proof of the consistency of PA. This is intriguing stuff, crisply and quite accessibly presented. The appendix is, however, suppressed in later editions (in fact, from the second onwards), even though there is plenty of room given to other materials and a new appendix

Now, a number of people have said that the appendix is one of the most interesting things about the book. I agree. I too remember being quite excited by it when I first came across it a long time ago!

So: has anyone heard a folkloric story about why Mendelson suppressed the appendix? I've never heard it suggested that there is a problem with the consistency proof as given.

Context, if you are interested: I asked this a couple of weeks ago on math.SE (without getting an answer) when starting to write up a survey of some of the Big Books on Mathematical Logic that will become part of my Teach-Yourself-Logic Guide (mostly for philosophers, though others might be interested), and I'd got to Mendelson. You can get the current version of the Guide by going to http://www.logicmatters.net/students/tyl/

• Here is a link to the math.SE question: math.stackexchange.com/q/288117 – Zev Chonoles Feb 12 '13 at 17:16
• Peter: in case you have not done so, I suggest that you also pose the question on FOM (on matters technico-historical one often gets better feed-back there). – Ali Enayat Feb 12 '13 at 17:55
• @AliEnayat Good thought! – Peter Smith Feb 12 '13 at 19:02
• @AliEnayat Can you give us the link to FOM ? – Duchamp Gérard H. E. Mar 12 '19 at 3:36
• @DuchampGérardH.E. FOM is an electronic mailing list; here is the link for it: cs.nyu.edu/mailman/listinfo/fom – Ali Enayat Mar 13 '19 at 6:10