Ok, I know I’m harping on this, but I really need submissions to the Carnival, which I’m posting Friday morning.  That means I need them Thursday night.  Please either go to the automated submission page on Blog Carnivals, or email submissions to me at siegelch[at]math[dot]upenn[edu], I’m up to six, but that’s still a pretty sad carnival.

Anything since June 13 is fair game, and I know that many of you have written some good things since then, and though not a carnival, I’m going to link to a bunch of them right now, asking you for permission to use your posts on Friday.

(I will not use any posts without explicit permission, so please email me if you want the post I picked out or something else used on Friday, this is merely a list of posts I found interesting)

The sum-product phenomenon in arbitrary rings

What’s a Stack?

The Carter-Gelsinger Eversion

Basic Category Theory I

A Variant of the Travelling Salesman Problem