Did the Train Reach its Destination: The Complexity of Finding a Witness
  Recently, Dohrau et al. studied a zero-player game on switch graphs and proved that deciding the termination of the game is in NP $\cap$ coNP. In this short paper, we show that the search version of this game on switch graphs, i.e., the task of finding a witness of termination (or of non-termination) is in PLS. 
Karthik C. S.
cs.CC cs.GT