Suggestion for page 298: Chapter 4.9, Exercises 12-13

[MetallicCrimson]

Granted, ex. 12 is simpler, but it would still be nice if it had a quick explanation similar to ex. 13.
Such that:
Proof. Since there are 6 edges, the total degree of such a graph has to be 6 · 2 = 12. Since all vertices have degree 3, there are 12/3 = 4 vertices.

(Also, it's nice how the only possible solution for ex. 12 is the complete graph for n=4. I don't think it should be mentioned, I just find it cool.)

[spamegg1]

Makes sense, I'll add that sentence.