Page 133, line 19-20: Replace "Jean Larson" by "C. C. Chang" Page 134, line 34: Replace "However, the (somewhat) related conjecture that for any graph H with chromatic number $n$, $r(H) \ge r(K_n)$ is still unresolved." by "However, the (somewhat) related conjecture was that for any graph H with chromatic number $n$, $r(H) \ge r(K_n)$. However, Faudree and McKay showed that this was falso for $n=4$, namley $r(K_4)=18>r(W_6)=17$, where $W_6$ is the $6$-wheel." Page 135, line 20: Replace "homothetic" by "congruent"