# Cookie seminar

**General Information**: Cookie seminar will take place on Mondays at 3:30 in the 9th floor lounge area. Talks should be of interest to the general math community, and generally will not run longer then 20 minutes. Everyone is welcome to talk, please just sign up on this page. Alternatively I will also sign interested people up at the seminar itself. As one would expect from the title there will generally be cookies provided, although the snack may vary from week to week.

To sign up please provide your name and a title. Abstracts are welcome but optional.

## Spring 2013

## Monday, January 29, Will Mitchell

Title: an unsolved graph isomorphism problem from plane geometry

Abstract: A geometric 4-configuration is a collection of $n$ lines and $n$ points in the Euclidean plane with the property that each of the lines passes through exactly four of the points, and each of the points lies on exactly four of the lines. No illustration of a 4-configuration appeared in print until 1980. The so-called "celestial configurations" are a well-behaved family of these objects. After discussing the construction and nomenclature of the celestial configurations, I'll describe an open problem regarding their graph-theoretical properties.