@Article{	  die87tcsa,
  author	= "Volker Diekert",
  journal	= "Theoretical Computer Science",
  pages		= "313--318",
  title		= "On some variants of the {E}hrenfeucht conjecture",
  volume	= "46",
  year		= "1987",
  doi		= "10.1016/0304-3975(86)90036-8"
}