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| Format: | Preprint |
| Published: |
2026
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| Online Access: | https://arxiv.org/abs/2602.13917 |
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| _version_ | 1866908835260661760 |
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| author | Wang, Shuwei |
| author_facet | Wang, Shuwei |
| contents | In many axiomatic set theories, Gödel's constructible universe $L$ is known as an inner model, that is, a definable class satisfying the same axioms (and containing the same ordinals). This gives a trivial proof that adding the axiom $V = L$ does not increase the consistency strength of the theory. In this paper, we shall look at a system of intuitionistic set theory known as $\mathrm{CZF}$, where $L$ fails to exhibit such nice properties. We will demonstrate that, here, the theory $\mathrm{CZF} + V = L$ is still equiconsistent with $\mathrm{CZF}$, but the proof will involve a much more complicated realisability model and a recursion-theoretic argument. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_13917 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | An equiconsistency proof for $\mathrm{CZF} + V = L$ Wang, Shuwei Logic Primary: 03E70, 03F25, Secondary: 03F55, 03D10 In many axiomatic set theories, Gödel's constructible universe $L$ is known as an inner model, that is, a definable class satisfying the same axioms (and containing the same ordinals). This gives a trivial proof that adding the axiom $V = L$ does not increase the consistency strength of the theory. In this paper, we shall look at a system of intuitionistic set theory known as $\mathrm{CZF}$, where $L$ fails to exhibit such nice properties. We will demonstrate that, here, the theory $\mathrm{CZF} + V = L$ is still equiconsistent with $\mathrm{CZF}$, but the proof will involve a much more complicated realisability model and a recursion-theoretic argument. |
| title | An equiconsistency proof for $\mathrm{CZF} + V = L$ |
| topic | Logic Primary: 03E70, 03F25, Secondary: 03F55, 03D10 |
| url | https://arxiv.org/abs/2602.13917 |