1. G. Chartrand, C. Egan, and P. Zhang, How to Label a Graph. Springer, New York (2019).
2. G. Chartrand, J. Hallas, E. Salehi, and P. Zhang, Rainbow mean colorings of graphs. Discrete Math. Lett. 3 (2020), 1–8.
3. G. Chartrand and P. Zhang, Chromatic Graph Theory. Second Edition. Chapman & Hall/CRC Press, Boca Raton (2020).
4. J. Hallas, Extremal Theory on Induced Graph Colorings. Doctoral Dissertation, Western Michigan University (2020).
5. J. Hallas, E. Salehi, and P. Zhang, Rainbow mean colorings of bipartite graphs. Bull. Insti. Combin. Appl.. 88 (2020), 78–97.