Thursday, June 20

4:00 PM

Mudd Hall Auditorium
Chair: Lars D. Andersen, Aalborg University, Denmark

## IP8

Graph Embedding

In 1890 Heawood gave an upper bound, called the Heawood number, for the number of colors needed to color a map (or graph) on the orientable surface of genus g. About 80 years later, Ringel and Youngs proved that Heawood's bound is tight. The Heawood number tends to infinity as g tends to infinity. In this presentation, the speaker will focus on the recent result that, for each fixed genus g, there are only finitely many obstructions for coloring a graph of genus g with only 5 colors.
**Carsten Thomassen**

Technical University of Denmark

*MEM, 4/10/96*