Since-clause

[Rustamsher]

Hello Alan,

I have a problem choosing the right grammar tense.

Context: Peter started doing something (reading a book) some time ago and still doing it. At a certain
moment of time when Peter was reading a book Mike started watching TV and he is still doing it. The two
actions are still in progress. Can I say?

Mike has been watching TV since Peter has been reading a book.

Can I use the present perfect progressive both in subordinate clause and the main clause like the sentence above?

Thanks.

[Alan]

Possible grammatically, but it means that the actions began at the same time, which is not your intended meaning. That would be better served by replacing 'since' with 'while', which would at least allow for the possibility of one action commencing after the other.