public static function hasInnerJoin(TimeSlot $a, TimeSlot $b) {
        $c1 = DateTimeHelper::isBetween($b->getStartDate(), $a->getStartDate(), $a->getEndDate());
        $c2 = DateTimeHelper::isBetween($b->getEndDate(), $a->getStartDate(), $a->getEndDate());
        $c3 = DateTimeHelper::isBetween($a->getStartDate(), $b->getStartDate(), $b->getEndDate());
        $c4 = DateTimeHelper::isBetween($a->getEndDate(), $b->getStartDate(), $b->getEndDate());
        return $c1 || $c2 || $c3 || $c4;
    }