Past exam of the computer science course of the University of Oxford / 2015 / Knowledge representation and reasoning / 3 / c / i / Solution

Use not for negation as failure, rather than classical logical negation. The disjunctive condition is expressed by two separate Datalog with negation rules:The positive $Year(x)$ premise restricts the rule to years and makes the variable explicitly safe. The divisibility relation is input data; the integer-looking constants do not make arbitrary arithmetic facts true automatically.