Lane A. Hemaspaandra Harald Hempel Arfst Nickelsen Algebraic Properties for P-Selectivity. 49-58 2001 conf/cocoon/2001 COCOON http://link.springer.de/link/service/series/0558/bibs/2108/21080049.htm db/conf/cocoon/cocoon2001.html#HemaspaandraHN01