It's a well-known open problem (Sophie-Germain primes) whether there are infinitely many primes $p$, $2p+1$. What about $p$, $2p-1$?

Seemingly it's also an open problem (see here and the linked question). I am aware that it is a special case of more general open problems.

But I'd like a concrete reference asserting that this specific problem is indeed open.

Edit: As I said, I'm not interested in more general conjectures. It's suitable for MO, because no one has given me a reference for this exact problem.

the fact that it is an open problem.But you could have just as well been interested in a discussion of methods or progress towards this problem. In the latter case the more general references would be helpful. Indeed, requests of the form: "I want more information on the problem." are in my experience more common than "I want it asserted it is open." $\endgroup$ – user9072 Oct 10 '15 at 19:47