3-Choosability of Triangle-Free Planar Graphs with Constraints on 4-Cycles

  • Authors:
  • Zdeněk Dvořák;Bernard Lidický;Riste Škrekovski

  • Affiliations:
  • rakdver@kam.mff.cuni.cz and bernard@kam.mff.cuni.cz;-;riste.skrekovski@FmF.uni-lj.si

  • Venue:
  • SIAM Journal on Discrete Mathematics
  • Year:
  • 2010

Quantified Score

Hi-index 0.00

Visualization

Abstract

A graph is $k$-choosable if it can be colored whenever every vertex has a list of at least $k$ available colors. We prove that if a triangle-free planar graph is not 3-choosable, then it contains a 4-cycle that intersects another 4- or 5-cycle in exactly one edge. This strengthens Thomassen's result [C. Thomassen, J. Combin. Theory Ser. B, 64 (1995), pp. 101-107] that every planar graph of girth at least 5 is 3-choosable. In addition, this implies that every triangle-free planar graph without 6- and 7-cycles is 3-choosable.