The two proofs are structurally very different, and don’t even prove the same conjecture. It’s becoming very clear that OpenAI did not steal anything here.
If it was "very clear", OpenAI wouldn't be threatening the researcher with "it's very bad for your career" or state "we can't tell you if it was trained on user input".
Additionally, according to the researcher, OpenAI's proof follows the same approach they used, and which was largely unused in academia, but OpenAI claimes they arrived at it immediately.
