@InProceedings{KP09,
   author =      "O. Kupferman and N. Piterman",
   title =       "Lower Bounds on Witnesses for Nonemptiness of Universal co-{B\"uchi} Automata",
   booktitle =    fossacs09,
   pages =       "182-196",
   year =        2009,
   volume =      "5504",
   series =      lncs,
   publisher = springer,
}