Bernd Borchert Lane A. Hemaspaandra Jörg Rothe Restrictive Acceptance Suffices for Equivalence Problems. 124-135 http://link.springer.de/link/service/series/0558/bibs/1684/16840124.htm 1999 conf/fct/1999 FCT db/conf/fct/fct99.html#BorchertHR99