Body-Plus Example

The "Body-Plus" instances are effectively solved by body-based and hybrid lookahead, but not by literal-based lookahead. Due to rule , either $x$ or $y$ must be contained in any answer set. Considering the additional program rules, body-based and hybrid lookahead detect that $y$ is underivable and that rule , where $n$ is the instance number, must be used for deriving $x$. That is, body-based and hybrid lookahead infer . In contrast, literal-based lookahead is unable to detect that alternative rules for $x$ and $y$ are unapplicable and that the body of must be true. Note that the instances are designed to mislead smodels' lookahead-based heuristics.