Why the domain layer is tigthly coupled to a framework dependency (RxJava) ?

Hi, here I am again, this time with a different concern.
Citing Uncle Bob's explanation of Use Cases:

> We also do not expect this layer (USE CASES) to be affected by changes to externalities such as the database, the UI, or any of the common frameworks. This layer is isolated from such concerns.

Your use cases depend on RxJava framework. I have to provide a Subscriber implementation in order to obtain List or a single User. I expect that a UseCase hides the implementation logic from the outside. To me, a UseCase is **Given** an id, **Return** a User.

Your case is Given an id **and a Subscriber implementation** return a User. What if at some point I don't want to use RxJava anymore? My UseCase shouldn't change! I have an id and I want a User back, but it still requires something depending on an external framework, meaning that I have to reimplement my UseCase even though nothing has changed, except for the framework it uses to accomplish the job.

Thank you @android10