3-coloring triangle-free planar graphs
Bernard Lidický
Department of Mathematics, Iowa State University, Ames, IA, USA
Department of Mathematics, Iowa State University, Ames, IA, USA
2017/3/7 Tue 4PM
A well known theorem of Grötzsch states that every planar graph is 3-colorable. We will show a simple proof based on a recent result of Kostochka and Yancey on the number of edges in 4-critical graphs. Then we show a strengthening of the Grötzsch’s theorem in several different directions. Based on joint works with Ilkyoo Choi, Jan Ekstein, Zdeněk Dvořák, Přemek Holub, Alexandr Kostochka, and Matthew Yancey.