Erdős problem #870 solved with ChatGPT-5.5-Pro and Lean
A user reported solving Erdős problem #870 using ChatGPT-5.5-Pro in combination with the Lean theorem prover, marking a notable application of AI-assisted formal mathematical reasoning.
Background
- Paul Erdős was a famously prolific 20th-century mathematician; "Erdős problems" are unsolved or open problems he posed, often with cash bounties. Problem #870 is one such conjecture no one had proven before.
- ChatGPT-5.5-Pro is a (likely fictional or satirical) future version of OpenAI's AI assistant; Lean is a real interactive theorem prover (proof assistant) widely used in formal mathematics, where a human writes a proof in a language the computer can verify line by line.
- This tweet appears to be satire or a hoax: no such problem exists in standard Erdős problem lists, and the version numbering ("5.5-Pro") mimics the naming conventions of AI model hype.
- It reflects a real cultural tension in math: some researchers believe AI + formal proof assistants will soon solve long-standing open problems, while skeptics call this fantasy until it actually happens.