@Article{	  dg98ai,
  title		= "Approximating Traces",
  journal	= "Acta Informatica",
  year		= "1998",
  volume	= "35",
  number2	= "7",
  pages		= "567--593",
  doi		= "10.1007/s002360050132",
  author	= "Diekert, Volker and Gastin, Paul"
}