1. Berge C., "Theory of Graphs and its Applications", Methuen, London, 1962.
2. Sanaa Kadum Kamal Yaseen," SOME KINDS OF MOBIUS FUNCTION GRAPHS ", Advanced Mathematical Models and Applications, Vol.7, no.1, pp.48–54, 2022.
3. An example in Beurling's theory of generalised primes
4. Examples of beurling prime systems
5. Thomas Hungerford, Abstract Algebra in introduction, Celeveland State University.