@inproceedings{DBLP:conf/sigir/Fraenkel81,
  author    = {Aviezri S. Fraenkel},
  title     = {Document Classification, Indexing and Abstracting May be
               Inherently Difficult Problems},
  booktitle = {SIGIR},
  year      = {1981},
  pages     = {77-82},
  ee        = {http://doi.acm.org/10.1145/511754.511766},
  crossref  = {DBLP:conf/sigir/81},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}

@proceedings{DBLP:conf/sigir/81,
  editor    = {Carolyn J. Crouch},
  title     = {Theoretical Issues in Information Retrieval, Proceedings
               of the Fourth International Conference on Information Storage
               and Retrieval,  Oakland, California, USA, May 31 - June
               2, 1981},
  publisher = {ACM},
  year      = {1981},
  isbn      = {0-89791-052-4},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}