public function setMinOperands($minOperands)
    {
        if (is_int($minOperands) && $minOperands >= 0) {
            $this->minOperands = $minOperands;
        } else {
            $msg = "The minOperands argument must be an integer >= 0, '" . $minOperands . "' given.";
            throw new InvalidArgumentException($msg);
        }
    }