@Article{	  db91ipl,
  author	= "Diekert, Volker and Book, Ronald V.",
  journal	= "Information Processing Letters",
  pages		= "21--23",
  title		= "On ``inherently context-sensitive'' languages -- {A}n
		  application of complexity cores",
  volume	= "40",
  year		= "1991",
  doi		= "10.1016/S0020-0190(05)80005-5"
}