@article{Skowronek-Kaziów:2009,
  author  = "J. Skowronek-Kaziów",
  title   = "Properties of digraphs connected with some congurence relations",
  journal = "Czechoslovak Mathematical Journal",
  volume  = "Vol. 59",
  number  = "no 1",
  pages   = "39--49",
  year    = "2009",
}