TypeScript: inconsistent factory signature (unable to declare custom dependencies)

I'm customizing mathjs extending its types and methods.
In JS I can register a type :
```js
factory('DateTime', ['typed'], function createDateTime({ typed }: { typed?: any }) {
typed.addType({
name: 'DateTime',
test: (x: any) => x && x.constructor.name === 'DateTime'
})
return DateTime
}),
```
and then use it as a dependency:
```js
factory('datetime', ['typed', 'DateTime'], function createDateTime({ typed, DateTime }) {}
```
but in TypeScript it's not possible - I'm getting:
Type '"DateTime"' is not assignable to type 'keyof MathJsStatic'.

PS> And BTW creating math object is also quite confusing in TypeScript:
```
import { create, all, factory } from 'mathjs';
const mathjs = create(all);
mathjs!.import!([ ... ]);
```