The chromatic number of the product of two 4-chromatic graphs is 4

Mohamed M. El-Zahar, Norbert Sauer. The chromatic number of the product of two 4-chromatic graphs is 4. Combinatorica, 5(2):121-126, 1985.

@article{El-ZaharS85,
  title = {The chromatic number of the product of two 4-chromatic graphs is 4},
  author = {Mohamed M. El-Zahar and Norbert Sauer},
  year = {1985},
  tags = {graph-rewriting, rewriting},
  researchr = {https://researchr.org/publication/El-ZaharS85},
  cites = {0},
  citedby = {0},
  journal = {Combinatorica},
  volume = {5},
  number = {2},
  pages = {121-126},
}