Evaluating 'help(not)' throws SyntaxError

For some reason, evaluating `help(not)` throws an error. For example:

```js
// Works fine
console.log(math.evaluate('help(and)'));

// "SyntaxError: Value expected (char 9)"
console.log(math.evaluate('help(not)'));
```

Please see this [jsfiddle](https://jsfiddle.net/aq6jygbk/) example.