Michael Bauland Martin Mundhenk Thomas Schneider Henning Schnoor Ilka Schnoor Heribert Vollmer The Tractability of Model-Checking for LTL: The Good, the Bad, and the Ugly Fragments http://arxiv.org/abs/0805.0498 2008 CoRR abs/0805.0498 db/journals/corr/corr0805.html#abs-0805-0498 informal publication