Structure of digraphs associated with quadratic congruences with composite moduli

@article{Somer2006StructureOD,
  title={Structure of digraphs associated with quadratic congruences with composite moduli},
  author={Lawrence Somer and Michal Kr{\'i}zek},
  journal={Discrete Mathematics},
  year={2006},
  volume={306},
  pages={2174-2185}
}