@Article{	  die93moebius,
  author	= "Volker Diekert",
  journal	= "Theoretical Computer Science",
  pages		= "25--43",
  title		= "{M}{\"o}bius functions and confluent semi-commutations",
  volume	= "108",
  year		= "1993",
  doi		= "10.1016/0304-3975(93)90229-M"
}