Christos Nomikos Panos Rondogiannis William W. Wadge Strong equivalence of logic programs under the infinite-valued semantics. 576-581 2009 109 Inf. Process. Lett. 11 http://dx.doi.org/10.1016/j.ipl.2009.02.002 db/journals/ipl/ipl109.html#NomikosRW09