@Book{lem2003sterntagebuecher, author = {Lem, Stanislaw}, title = {Sterntagebücher}, year = {2003}, number = {}, url = {http://www.amazon.de/exec/obidos/ASIN/3518455346/}, const = {\ text} } @Book{baeza-yates1999modern, author = {Baeza-Yates, Ricardo A. and Ribeiro-Neto, Berthier}, title = {Modern Information Retrieval}, year = {1999}, number = {}, url = {http://portal.acm.org/citation.cfm?id=553876}, const = {\ text} }