He wrote a significant paper on the series of chromatic numbers and Brooks' theorem, titled Hajós graph coloring conjecture: variations and counterexamples.
From 1972 to 1973, he was a research and teaching assistant at Ohio State University, where he earned the Master of Science degree in Mathematics.
[1] In 1976, he went to work at Wayne State University, where he concentrated the research on chromatic numbers and Brooks' theorem.
, which led to the joint paper written with Paul Erdős and Béla Bollobás titled Hadwiger's conjecture is true for almost every graph.
[3] He co-authored scholarly papers with Arthur M. Hobbs,[6] Béla Bollobás and Paul Erdős,[5] Hong-Jian Lai, Zheng-Yiao Han, and Yehong Shao,[6] among others.