Logical Symbols

• 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);
• neg/1 (and -/1) are prefix predicates standing for classical negation;
• not/1 (and ~/1) are prefix predicates standing for negation as failure;
• ,/2 is conjunction;
• ;/2 (or v/2 or |/2) is disjunction;
• :-/2 is used for describing rules in the usual way.