Aggregate Functions in Disjunctive Logic Programming: Semantics, Complexity, and Implementation in DLV.

Tina Dell'Armi Wolfgang Faber Giuseppe Ielpa Nicola Leone Gerald Pfeifer Aggregate Functions in Disjunctive Logic Programming: Semantics, Complexity, and Implementation in DLV. 847-852 2003 conf/ijcai/2003 IJCAI db/conf/ijcai/ijcai2003.html#DellArmiFILP03