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AI's solution to 87-year-old riddle takes mathematicians by surprise

A mathematician at Harvard University, Levent Alpöge, has used AI to disprove the 87-year-old Jacobian conjecture, posting a 216-character counterexample on X on 19 July. The solution, which relied on Anthropic's Claude Fable 5, is considered the most difficult mathematical problem yet solved by AI, according to experts. Abhishek Saha at Queen Mary University of London called it a "pretty big deal" and the biggest conjecture AI has played a significant role in so far.

read3 min views4 publishedJul 21, 2026
AI's solution to 87-year-old riddle takes mathematicians by surprise
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A mathematician has cracked an 87-year-old conundrum with the help of AI and announced the solution unceremoniously in a tweet. The finding is the most difficult mathematical problem yet solved by AI, say experts.

Levent Alpöge at Harvard University wrote on X on 19 July that the Jacobian conjecture – which academics have spent decades trying to prove was true – is actually false, giving a tiny, 216-character counterexample as proof.

The Jacobian conjecture – which suggests that a certain type of mathematical function would also work in reverse – was formally set out by Ott-Heinrich Keller in 1939. It was also on an influential list of 18 fiendishly difficult problems for mathematicians to tackle in the 21st century drawn up by Stephen Smale in 1998.

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Alpöge did not respond to New Scientist’s request for interview, but said in his tweet that part of the work was down to his “close friend fable”- seemingly referring to AI company Anthropic’s Claude Fable 5. Alpöge thanked Fable for working during the World Cup final.

Anthropic did not respond to a request for comment.

Abhishek Saha at Queen Mary University of London says AI’s recent advances in mathematics, such as the OpenAI model that recently cracked a decades-old conjecture by Paul Erdős, have been surprising, but this latest finding has stepped things up significantly.

“Probably this is the biggest conjecture that AI has played a significant role [in proving or disproving] so far in mathematics,” he says. “This is a pretty big deal. AI has [made] remarkable progress in the last year.”

The single line of mathematics posted by Alpöge was simple to verify and many mathematicians have already done so, says Saha. Now the big question is how it was done.

“There are some problems that are very hard to solve but once a solution is there, they are relatively easy to check. So this is like that,” he says. “I don’t know how he did it, what exactly was the prompt to give Fable, because if one were to search everything, it wouldn’t quite work, so obviously there was some insight also which is not currently published.”

Saha says both the appearance and the nature of the result is a surprise. “People have been trying to prove it [the Jacobian conjecture] because it sounds, intuitively, very true. I don’t think that many people have been trying to disprove it. And now we have this one-sentence counterexample,” he says.

There are still open questions, says Saha. For example, this new counterexample disproves the conjecture with three variables, but a version with two variables could theoretically still be true.

Chris Bowman-Scargill at the University of York, UK, says mathematicians have in some ways already adjusted to the shocking new capabilities of AI, but there is a difference between finding counterexamples that disprove conjectures and building whole new branches of mathematics, which still requires human creativity.

“If you look at Fermat’s last theorem [which was solved by Andrew Wiles in 1994], you had to create a hundred pages of new mathematics – you had to build a whole big theory in order to solve a conjecture,” says Bowman-Scargill. “And often the interesting stuff in maths isn’t ‘oh, we’ve ticked off this conjecture, yay’, it’s more the stuff you have to build along the way in order to solve the conjecture.”

“I think [AI] has sort of proven that it can do this, so you’re now like, OK, what next?,” he says.

Ivan Fesenko at Westlake University in China believes what comes next is increasingly capable AI models that will solve ever more complex problems, disrupting the field as they go.

“Right now, AI can already produce master’s degrees in mathematics. In one year, they will produce PhD degrees in mathematics. And then the question arises, do we really need so many mathematicians around if AI can do such things so nicely?” says Fesenko. “So basically we’re talking about fundamental change in mathematics.”

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