@InProceedings{	  die92kyotows,
  author	= "Volker Diekert",
  booktitle	= "{W}ords, {L}anguages and {C}ombinatorics (Kyoto, Japan
		  1990)",
  editor	= "M. Ito",
  pages		= "119--130",
  publisher	= "World Scientific, Singapore",
  title		= "{M}{\"o}bius functions and confluent semi-commutation
		  systems",
  year		= "1992",
  doi		= "10.1016/0304-3975(93)90229-M"
}