* a relation not mapped by this.instance
*/
public TupleSet evaluate(Expression expression){
if (expression == null) throw new NullPointerException("expression");
final BooleanMatrix sol = Translator.evaluate(expression,instance,options);
return instance.universe().factory().setOf(expression.arity(), sol.denseIndices());
}
/**
* Evaluates the specified int expession with respect to the relation-tuple mappings
* given by this.instance and using this.options.