Seminar of Graph Theory - František Kardoš (12.11.2020)
Thursday 12.11.2020 at 9:50
By: Martin Škoviera
František Kardoš (FMFI UK, LABRI University of Bordeaux):
On the 4-color theorem for signed graphs
Termín: 12.11.2020, 9:50 hod.
MS TEAMS code (users from Comenius University in Bratislava): gglxxc7
Link (guests outside Comenius University in Bratislava)
Macajova, Raspaud and Skoviera defined the chromatic number of a signed graph which coincides for all-positive signed graphs with the chromatic number of unsigned graphs. They conjectured that in this setting, for signed planar graphs four colors are always enough, thereby generalising The Four Color Theorem. We disprove the conjecture.