This is Gödel's ontological proof, which is fully explained on Wikipedia (see the link).
I find this to be an incredible easter egg, since the proof is something which Sheldon says he doesn't understand. And Sheldon has expressed more than once that he doesn't believe in the existence of god.
(Originally I thought this would be something pertaining to the many-worlds interpretation of quantum mechanics, which was brought up a couple of scenes before this showed up. But upon re-examination of the screenshot, it didn't seem that way anymore.)