[FOM] Mendelson's missing appendix on the consistency of PA

[Peter Smith]

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/
-- 
Dr Peter Smith: Faculty of Philosophy, University of Cambridge