1. Show that radG ≤ diamG ≤ 2radG for every graph G.
Hint: Estimate the distances within G as seen from a central vertex.
2. Prove the weakening of Theorem 1.3.4 obtained by replacing average with minimum degree. Deduce that | G | ≥ n0(d/2, g) for every graph G as given in the theorem.
Hint: Count vertices as in the proof of Proposition 1.3.3. For the even case, start with two adjacent vertices.
3. Show that a connected graph of diameter k and minimum degree d has at least about kd/3 vertices but need not have substantially more.
Hint: Pick two vertices x, y of maximum distance, and show that many of the distance classes Di from x have to be large.