@InProceedings{	  dor91icalp,
  author	= "Volker Diekert and Edward Ochma{\'n}ski and Klaus
		  Reinhardt",
  address	= "Heidelberg",
  booktitle	= "Proc. 18th International Colloquium Automata, Languages
		  and Programming (ICALP'91), Madrid",
  editor	= "J. Leach-Albert and B. Monien and M. Rodriguez Artalejo",
  note		= "Journal version in Information and Computation, 1994",
  volume	= "510",
  pages		= "229--241",
  publisher	= "Springer-Verlag",
  series	= "Lecture Notes in Computer Science",
  title		= "On confluent semi-commutation systems --- decidability and
		  complexity results",
  year		= "1991",
  doi		= "10.1007/3-540-54233-7_137"
}