referenced not cited:
%  \bibitem{2} R. L. Graham and B. L. Rothschild, A short proof of van der Waerden's theorem on arithmetic progressions, \emph{Proc. Amer. Math. Soc.} \textbf{42} (1974), 385--386.
%  \bibitem{6} B. L. van der Waerden, Beweis einer Baudetshen Vermutung, \emph{Nieuw Arch. Wisk.} \textbf{15} (1927), 212--216.