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.