Solutions and Hints for some of the Exercises
3.1 For \(A \subseteq V(G)\) let f(A) be the number of edges between A and \( V(G)/A \). Let A be such that f(A) is maximal. No vertex \(\nu \in A\) has more neighbors in A than in V(G)\A as we would have f\((A-\nu) > A\).
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