Syntax

• true/0 is a predefined fact (that is used for dlv in order to make facts go into the intentional database);
• false/0 is a predefined symbol never to be found in any answer set (used for defining classical negation via integrity constraints);
• not/1 are prefix predicates standing for negation as failure;
• ,/2 is conjunction;
• ;/2 is disjunction;
• :-/2 is used for describing rules in the usual way.