@InProceedings{	  die85stacs,
  author	= "Volker Diekert",
  address	= "Heidelberg",
  booktitle	= "Proc. 2nd Annual Symposium on Theoretical Aspects of
		  Computer Science (STACS'85), Saarbr{\"u}cken (Germany),
		  1985",
  editor	= "K. Mehlhorn",
  volume	= "182",
  pages		= "87--97",
  publisher	= "Springer-Verlag",
  series	= "Lecture Notes in Computer Science",
  title		= "On {H}otz groups and homomorphic images of sentential form
		  languages",
  year		= "1985",
  doi		= "10.1007/BFb0023998"
}