feat(CombinatoryLogic): SKI terms for Nat.sqrt, Nat.pair, and Nat.unpair - #445
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Implement SKI combinator terms for three Mathlib numeric operations and prove they compute the correct values on Church numerals: - Sqrt / sqrt_correct: integer square root via root-finding - NatPair / natPair_correct: Nat.pair via case split on a < b - NatUnpairLeft / natUnpairLeft_correct: left projection of Nat.unpair - NatUnpairRight / natUnpairRight_correct: right projection of Nat.unpair
chenson2018
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Mar 20, 2026
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Thanks for splitting this out! It did make it easier to look at.
Two general comments (probably for later PRs):
- We use the
SKInamespace explicitly a lot in this module, maybe more readable if we didn't - I think more generally a syntax for SKI might be nice for readability. The docstrings you have listing these out helps show precisely what we'd want.
Co-authored-by: Chris Henson <46805207+chenson2018@users.noreply.github.com>
Co-authored-by: Chris Henson <46805207+chenson2018@users.noreply.github.com>
Co-authored-by: Chris Henson <46805207+chenson2018@users.noreply.github.com>
Co-authored-by: Chris Henson <46805207+chenson2018@users.noreply.github.com>
Co-authored-by: Chris Henson <46805207+chenson2018@users.noreply.github.com>
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LGTM. Is this ready to merge @jessealama? I wasn't sure since it's still marked as a draft.
jessealama
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March 20, 2026 05:51
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Apr 6, 2026
…air (leanprover#445) Implement SKI combinator terms for Nat.sqrt, Nat.pair, and Nat.unpair with correctness proofs against Mathlib definitions. Split out from leanprover#403 to make review easier. --------- Co-authored-by: Chris Henson <46805207+chenson2018@users.noreply.github.com>
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Apr 22, 2026
…air (leanprover#445) Implement SKI combinator terms for Nat.sqrt, Nat.pair, and Nat.unpair with correctness proofs against Mathlib definitions. Split out from leanprover#403 to make review easier. --------- Co-authored-by: Chris Henson <46805207+chenson2018@users.noreply.github.com>
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Jun 14, 2026
…air (leanprover#445) Implement SKI combinator terms for Nat.sqrt, Nat.pair, and Nat.unpair with correctness proofs against Mathlib definitions. Split out from leanprover#403 to make review easier. --------- Co-authored-by: Chris Henson <46805207+chenson2018@users.noreply.github.com>
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…icts - Chain the three fix tasks to eliminate mutual file conflicts: 445 (conservativity proof) -> 446 (citations/bib) -> 444 (uniformity sweep). - Scope Temporal/Tableau/ OUT of 444 (owned by the active 301/426/439 tableau redesign line) to avoid collision. - leanprover#445 now supersedes leanprover#275; abandon leanprover#275 (goal subsumed by the no-sorry conservativity proof). - Repoint task leanprover#414 (Modal/Temporal/Bimodal proof simplification) off the abandoned leanprover#275 and onto 444/445/446 so it sequences after this cleanup. Session: sess_1782882070_293303
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Implement SKI combinator terms for Nat.sqrt, Nat.pair, and Nat.unpair with correctness proofs against Mathlib definitions.
Split out from #403 to make review easier.