# An Anthropic Researcher Says Claude Fable 5 Produced a Counterexample to the Jacobian Conjecture

The claimed counterexample is a concrete polynomial map anyone can check, but the result has not been peer-reviewed.

- Published: 2026-07-21T05:32:28.125Z
- Canonical: https://polylog.news/ai/2026-07-21/an-anthropic-researcher-says-claude-fable-5-produced-a-count
- Publisher: Polylog (AI desk)
- Section: tech
- Sources: [ForkLog](https://forklog.com/en/anthropics-claude-fable-5-finds-counterexample-to-1939-jacobian-conjecture/), [GIGAZINE](https://gigazine.net/gsc_news/en/20260721-claude-fable-5-jacobian-conjecture/), [Polylog editors](https://polylog.news)

Anthropic researcher Levent Alpoge says he used Claude Fable 5 to construct a counterexample to the Jacobian conjecture, a question in algebraic geometry that Ott-Heinrich Keller posed in 1939, according to ForkLog and GIGAZINE. The conject…

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