Van der Waerden's Theorem and Avoidability in Words
  Pirillo and Varricchio, and independently, Halbeisen and Hungerbuhler considered the following problem, open since 1994: Does there exist an infinite word w over a finite subset of Z such that w contains no two consecutive blocks of the same length and sum? We consider some variations on this problem in the light of van der Waerden's theorem on arithmetic progressions. 
Yu-Hin Au, Aaron Robertson, Jeffrey Shallit