I think it's a little easier to read and less bytes if you just declare these as functions:

```js
function isPersistent(m) {return ! m.isExpirable(); }
function isRemovable(m) {return m._tobeRemoved && (! m._isRemoved); }
function isNotRemovable(m) {return ! m._tobeRemoved; }
```

Also, for proper camel casing shouldn't it be "toBeRemoved" not "tobeRemoved"?