public function setIncludeLowerBound($includeLowerBound)
    {
        if (is_bool($includeLowerBound)) {
            $this->includeLowerBound = $includeLowerBound;
        } else {
            $msg = "The includeLowerBound argument must be a boolean, '" . gettype($includeLowerBound) . "' given.";
            throw new InvalidArgumentException($msg);
        }
    }