Keeping Your Distance is Hard
  We study the computational complexity of distance games, a class of combinatorial games played on graphs. A move consists of colouring an uncoloured vertex subject to it not being at certain distances determined by two sets, D and S. D is the set of forbidden distances for colouring vertices in different colors, while S is the set of forbidden distances for the same colour. The last player to move wins. Well-known examples of distance games are Node-Kayles, Snort, and Col, whose complexities were shown to be PSPACE-hard. We show that many more distance games are also PSPACE-hard. 
Kyle Burke, Silvia Heubach, Melissa Huggan, and Svenja Huntemann
cs.CC math.CO