public function process()
    {
        $operands = $this->getOperands();

        if ($operands->containsNull() === true) {
            return null;
        }

        if ($operands->exclusivelySingle() === false) {
            $msg = "The Lte operator only accepts operands with a single cardinality.";
            throw new OperatorProcessingException($msg, $this, OperatorProcessingException::WRONG_CARDINALITY);
        }

        if ($operands->exclusivelyNumeric() === false) {
            $msg = "The Lte operator only accepts operands with a float or integer baseType.";
            throw new OperatorProcessingException($msg, $this, OperatorProcessingException::WRONG_BASETYPE);
        }

        return new QtiBoolean($operands[0]->getValue() <= $operands[1]->getValue());
    }