1. A.A. Kosinski, Differential Manifolds (Dover, Mineola, 1993)
2. J.W. Milnor, Topology from the Differential Viewpoint (Princeton University Press, Princeton, 1997)
3. R. Diestel, Graph Theory (Springer, Heidelberg, 2012)
4. A.E. Brouwer, W.H. Haemers, Spectra of Graphics (Springer, New York, 2010)
5. D. Cvetković, P. Rowlinson, S. Simić, An Introduction to the Theory of Graph Spectra (Cambridge University Press, Cambridge, 2010)