@InCollection{	  Petersen06scl,
  author	= "Holger Petersen",
  title		= "Computable Lower Bounds for Busy Beaver Turing Machines",
  booktitle	= "Recent Advances in Formal Languages and Applications",
  publisher	= "Springer-Verlag",
  year		= "2006",
  volume	= "25",
  editor	= "{\'E}sik, Zolt{\'a}n and Martin-Vide, Carlos and Mitrana,
		  Victor",
  pages		= "305--319",
  series	= "Studies in Computational Intelligence",
  doi		= "10.1007/978-3-540-33461-3_12"
}