private static function optional($feature) {
        if ($feature->getParent())
            return Logic::implies(Logic::is($feature), Logic::is($feature->getParent()));
    }
private static function optional($feature) {
        if ($feature->getParent())
            return Logic::implies(Logic::is($feature), Logic::is($feature->getParent()));
    }
private static function optional ( $ feature ) { if ( $ feature -> getParent ( ) ) return Logic :: implies ( Logic :: is ( $ feature ) , Logic :: is ( $ feature -> getParent ( ) ) ) ; }
Semantics for an optional feature.
If an optional feature is selected, its parent is selected.
@param Feature $feature
@return callable
Semantics for an optional feature . If an optional feature is selected its parent is selected .