Plane graphs without 4- and 5-cycles and without ext-triangular 7-cycles are 3-colorable

Ligang Jin, Yingli Kang, Michael Schubert +1

Listed as No. 53 among the one hundred famous unsolved problems in [J. A. Bondy, U. S. R. Murty, Graph Theory, Springer, Berlin, 2008] is Steinberg's conjecture, which states that…