1. Every planar graph is four colorable. Part I. Discharging;Appel;Illinois J. Math.,1977
2. Every planar graph is four colorable. Part II. Reducibility;Appel;Illinois J. Math.,1977
3. Planar graphs with neither 5-cycles nor close 3-cycles are 3-colorable;Borodin;J. Graph Theory,2010
4. Planar graphs without cycles of length from 4 to 7 are 3-colorable;Borodin;J. Combin. Theory Ser. B,2005
5. A sufficient condition for planar graphs to be 3-colorable;Borodin;J. Combin. Theory Ser. B,2003