@article{gmr-usog-08, 
author = "B. G{\"a}rtner and W.~D. Morris{, Jr.} and L. R{\"u}st", 
title =	"Unique Sink Orientations of Grids", 
journal = "Algorithmica", 
volume = "51",
issue = "2",
pages = "200--235",
year = "2008" 
}