Where to learn Combinatorics & Graph Theory further? So far I have learned this subject for 1 year, and I really enjoyed it, I found the theorems and proofs very interesting, but the subject is over. I want to ask your opninion, where could I learn it further, and what may be still worth to know about, since I find this subject very useful in many mathematical problems, and I may never know, when I could use this knowledge in the future. :)
So, in my two semesters, at first, we learnt about the basic definitions, and after that, we started planar graphs, perfect graphs, chromatic number, Ramsey, and Turán-related theorems, and we finished with Hypergraphs(theorems like Fisher Inequality, and Erdos-Ko-Rado theorem). 
If you can recommend a book, or an online site, where I can learn things, which are still "worth" to learn about, please tell me about it! Thanks in advance.
 A: There are a lot of different directions you could go depending on what really interested you the most. Here are a few ideas:


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*Diestel has a few chapters you might find interesting. Chapter 8 on Infinite Graphs, Chapter 11 on Random Graphs, and Chapter 12 provides an especially good overview of the Graph Minor Theorem.

*Mohar and Thomassen's Graphs on Surfaces is a great book on topological graph theory.

*Bollobás's Extremal Graph Theory builds on the Ramsey and Turán results you learned. 

*Bollobás's Random Graphs builds on Diestel's chapter, if you enjoy that. 

*Godsil & Royle have a good introductory book for Algebraic Graph Theory.

*Oxley's Matroid Theory is a great reference for the subject, and there are a ton of really interesting, deep results related to graph theory.
I would also suggest talking to professors at your University that work on graph theory and combinatorics. You might be able to do a reading course in the subject, or even some of your own original research. Graph theory is fairly easy to start research as an undergrad, compared to other topics. 
