Markus Holzer Martin Kutrib Nondeterministic Finite Automata-Recent Results on the Descriptional and Computational Complexity. 1-16 2008 CIAA http://dx.doi.org/10.1007/978-3-540-70844-5_1 conf/wia/2008 db/conf/wia/ciaa2008.html#HolzerK08