Inverse Roles Make Conjunctive Queries Hard

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\begin{bibtex} @inproceedings{DBLP:conf/dlog/Lutz07,

 author    = {Carsten Lutz},
 title     = {Inverse Roles Make Conjunctive Queries Hard},
 booktitle = {Description Logics},
 year      = {2007},
 ee        = {http://ceur-ws.org/Vol-250/paper_3.pdf},
 crossref  = {DBLP:conf/dlog/2007},
 bibsource = {DBLP, http://dblp.uni-trier.de}

}

\end{bibtex}