@techreport{FichteSzeider12,
 author = {Johannes Klaus Fichte and Stefan Szeider},
 institution = {Arxiv.org},
 note = {Extended and updated version of a paper that
appeared in the proceedings of IJCAI 2011, the 22nd
International Joint Conference on Artificial
Intelligence},
 number = {1104.2788},
 title = {Backdoors to Tractable Answer-Set Programming},
 year = {2012}
}