@article{GDZPPN002207133,
title = {The diameter of the character degree graph..},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {394},
year = {1989},
pages = {181-198},
zbl = {0678.20002},
url = {http://dml.mathdoc.fr/item/GDZPPN002207133}
}
Willems, W.; Manz, O.; Wolf, Th.R. The diameter of the character degree graph... Journal für die reine und angewandte Mathematik, Tome 394 (1989) pp. 181-198. http://gdmltest.u-ga.fr/item/GDZPPN002207133/