feat(CombinatoryLogic): SKI terms for Nat.sqrt, Nat.pair, and Nat.unpair#445
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chenson2018 merged 9 commits intoleanprover:mainfrom Mar 20, 2026
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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
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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.
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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.