I am trying to invert the product rule in the following situation:

`ex := \partial_{a}{A} B + 2 A \partial_{a}{B}`

(update: here I stress the **extra factor of 2** in front of the last term)

and I tried the command

```
substitute(ex, $\partial_{a?}{A??} B?? + A?? \partial_{a?}{B??}
-> \partial_{a?}{A?? B??}$);
```

but it does not work. I don't want to do this one by one as there are many terms like this in my calculation.

I wonder if there's a method that I can unwrap

`2 A \partial_{a}{B} -> A \partial_{a}{B} + A \partial_{a}{B}`

so that these can be tackled individually?

Thanks very much!