Nikolay Pelov Miroslaw Truszczynski Semantics of disjunctive programs with monotone aggregates - an operator-based approach. 327-334 2004 conf/nmr/2004 NMR http://www.pims.math.ca/science/2004/NMR/papers/paper43.pdf db/conf/nmr/nmr2004.html#PelovT04