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arXiv · 2606.12462

Auto formalisation of Chaitin and of the surprise incompleteness Theorem

Thierry Coquand
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Abstract

This is a continuation of a previous report on an experiment in autoformalisation of G\"odel's second incompleteness theorem in Agda using Claude. Using the framework built in this experiment, Claude could ``automformalise'' Chaitin's proof of the first incompleteness theorem and then the Kritchman-Raz surprise examination paradox version of the second incompleteness. As the first experiment, the project provides a case study of the strengths and limitations of current large language models in mathematics. Since Chaitin's proof involves coding programs, Claude had to represent code as ternary string and could build autonomously a parser and a continuation stack evaluation machine. The fact that we can simulate computations as expected is not completely trivial and we suggested a Gandy/Howard majorisation argument, that Claude had no problem to follow. The resulting formalisation clarifies a number of details left implicit in the original presentation and provides a fully machine-checked proof of these arguments for Church's Basic Recursive Arithmetic.

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Thierry Coquand. 2026-06-09. Auto formalisation of Chaitin and of the surprise incompleteness Theorem. https://arxiv.org/abs/2606.12462

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