M. Ortiz de la Fuente, S. Rudolph, M. Simkus:
"Query Answering is undecidable in DLs with regular expressions, inverses, nominals, and counting";
Report for TU Wien, Institut für Informationssysteme; Report No. INFSYS RR 1843-10-03, 2010; 18 pages.
http://www.kr.tuwien.ac.at/research/reports/rr1003.pdf