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arXiv · 2607.21187

Case study: proving sqrt(2) irrational with LPTP and an LLM

Fred Mesnard·Étienne Payet·Wim Vanhoof
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Abstract

We present the interactions with an LLM (Large Language Model) aiming at proving that the square root of 2 is not a rational number in an LP (Logic Programming) context. We start from a few basic pure logic programming predicate definitions. We rely on the LPTP (Logic Program Theorem Prover) system for stating and proving properties about logic programs. As the proof language of LPTP is based on natural deduction, the proofs are human readable. In our case study, we sketch in LPTP the usual proof showing the irrationality of the square root of 2. Then we describe the interactions we had with the LLM. We end up with a complete formal proof, partially generated by an LLM and fully proof-checked by LPTP.

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Fred Mesnard, Étienne Payet, Wim Vanhoof. 2026-07-23. Case study: proving sqrt(2) irrational with LPTP and an LLM. https://doi.org/10.4204/eptcs.450.5

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