@misc{NipkowT-urexp,
  author =       {Tobias Nipkow and Dmitriy Traytel},
  title =        {Unified Decision Procedures for Regular Expression
                  Equivalence},
  year =         2014,
  howpublished = {\url{http://www.in.tum.de/~nipkow/pubs/regex_equiv.pdf}}
}
