Conversation

It's easy to prove that you have a piece of data and when you first got it. What's harder to prove is that you *don't* have a piece of data. Equally hard is to prove that you had a piece of data *first*, because that requires proving that nobody else had it before. The philosophers say that proving that something doesn't exist is impossible, so if that's the problem you're trying to solve, you have to reframe it.