@InProceedings{	  Petersen97mfcs,
  author	= "Petersen, Holger",
  title		= "Homomorphic Images of Sentential Forms and Terminating
		  Grammars",
  year		= "1997",
  volume	= "1295",
  pages		= "448--457",
  publisher	= "Springer",
  address	= "Berlin",
  series	= "Lecture Notes in Computer Science",
  booktitle	= "22nd International Symposium, MFCS'97, Bratislava,
		  Slovakia, August 25-29, 1997, Proceedings",
  doi		= "10.1007/BFb0029988"
}