private static function mandatory($feature) {
        if ($feature->getParent() && $feature->getMandatory())
            return Logic::equiv(Logic::is($feature), Logic::is($feature->getParent()));
    }
private static function mandatory($feature) {
        if ($feature->getParent() && $feature->getMandatory())
            return Logic::equiv(Logic::is($feature), Logic::is($feature->getParent()));
    }
private static function mandatory ( $ feature ) { if ( $ feature -> getParent ( ) && $ feature -> getMandatory ( ) ) return Logic :: equiv ( Logic :: is ( $ feature ) , Logic :: is ( $ feature -> getParent ( ) ) ) ; }
Semantics for a mandatory feature.
A mandatory feature is selected iff its parent is selected.
@param Feature $feature
@return callable
Semantics for a mandatory feature . A mandatory feature is selected iff its parent is selected .