public function removeTimeSlot(TimeSlot $timeSlot) {
        for ($i = count($this->timeSlots) - 1; 0 <= $i; --$i) {
            if (true !== TimeSlotHelper::equals($timeSlot, $this->timeSlots[$i])) {
                continue;
            }
            unset($this->timeSlots[$i]);
        }
        return $this;
    }