src/Logic/Not.php
public function toString()
    {
        $exprString = $this->expr->toString();

        if (isset($exprString[0]) && '(' === $exprString[0]) {
            return 'not'.$exprString;
        }

        return 'not('.$exprString.')';
    }
public function toString()
    {
        $exprString = $this->expr->toString();

        if (isset($exprString[0]) && '(' === $exprString[0]) {
            return 'not'.$exprString;
        }

        return 'not('.$exprString.')';
    }
{@inheritdoc}