@BOOK{bangjensen2009digraphs,
  title = {Digraphs: Theory, Algorithms and Applications},
  publisher = {Springer},
  year = {2009},
  author = {Jørgen Bang-Jensen and Gregory Z. Gutin},
  edition = {2},
}

@BOOK{diestel2010graph,
  title = {Graph Theory},
  publisher = {Springer},
  year = {2010},
  author = {Reinhard Diestel},
  volume = {173},
  series = {Graduate Texts in Mathematics},
  edition = {4},
  note = {\url{http://diestel-graph-theory.com}},
  isbn = {978-3-642-14278-9}
}

@INCOLLECTION{harary1974nullgraph,
  author = {Harary, Frank and Read, RonaldC.},
  title = {Is the null-graph a pointless concept?},
  booktitle = {Graphs and Combinatorics},
  publisher = {Springer Berlin Heidelberg},
  year = {1974},
  editor = {Bari, RuthA. and Harary, Frank},
  volume = {406},
  series = {Lecture Notes in Mathematics},
  pages = {37-44},
  doi = {10.1007/BFb0066433},
  isbn = {978-3-540-06854-9},
  url = {https://doi.org/10.1007/BFb0066433}
}
