Variable Set Theory?

Mike Barr posted in the cats mailing list the following:
Around 1986, Colin McLarty, Charles Wells, and I noticed that Scientific American had recently published a few articles on subjects mathematical
and decided to try to write one on variable set theory, AKA topos theory.
Unfortunately, that particular window at Sci Am quickly closed.  Our article was turned down and we forgot about it.  More recently, I decided it might be interesting, or at least amusing to throw it open to the
categorical community.  The result can be found at
ftp://ftp.math.mcgill.ca/barr/pdffiles/vst.pdf

(the picture is apparently Grothendieck lifting Michael Atiyah, from facebook, so who knows if it's real...)


Further news: Since the ftp site in Montreal is having some issues at the moment, Mike Barr was kind enough to send us a copy of the paper, which I'm posting here. Thanks Mike!

Set Theory for the Masses

So I've posted something about the two currents in Set Theory trying to add more axioms to solve the Continuum Hypothesis and the guys had more than a hundred comments on the post, so they are even starting to write a new paper on the subject, yay!

In some ways this is all I have always advocated for: maths needs to be done collectively, social networks can have an effective role in creating new knowledge by putting people in contact with others, etc..

But the Facebook post is not ideal: you cannot write maths properly, you cannot comment where you want, and let's face it, I cannot cope with the speed that they're producing ideas/thesis/hypotheses and demolitions. Maybe this is because I'm not a set-theorist, maybe it's because my full time job is not as a mathematician, maybe is just because I'm getting old. Who knows?
Anyways in an attempt to parse their conversation and get my own ideas straightened I've created another blog http://settheory4themasses.blogspot.com/2013/12/all-you-didnt-want-to-know-about-set.html