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feat(Logic): semantic consequence, with Kleene K3 as an instance - #1156

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jessealama wants to merge 11 commits into
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jessealama:kleene-propositional
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jessealama wants to merge 11 commits into
leanprover:mainfrom
jessealama:kleene-propositional

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@jessealama jessealama commented Oct 22, 2026 •

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This PR adds a logical consequence relation for inference systems whose judgements pair a model with a proposition, and instantiates it for Kleene's strong three-valued logic. The relation has weakening and cut, and contradictory premises entail everything, as usual; these are proved once, generically, over a class of models given as judgemental contexts. However, in K3 the deduction theorem fails: A entails A, but A → A is not valid for ⊥-free A.

Kleene consequence is strictly weaker than classical consequence. Restricting to two-valued valuations gives ClassicalEntails, which Entails implies. Excluded middle separates the two.

I used Claude to help write some of the code.

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jessealama force-pushed the kleene-propositional branch 5 times, most recently from 931d84e to b5d5e23 Compare October 23, 2026 08:29
@jessealama jessealama changed the title feat(Logic): consequence in Kleene and evaluation of propositional logic feat(Logic): consequence in Kleene K3 Oct 23, 2026
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jessealama force-pushed the kleene-propositional branch from d9915ae to a3d8c5a Compare October 23, 2026 17:42
@jessealama jessealama changed the title feat(Logic): consequence in Kleene K3 feat(Logic): semantic consequence, with Kleene K3 as first instance Oct 23, 2026
@jessealama jessealama changed the title feat(Logic): semantic consequence, with Kleene K3 as first instance feat(Logic): semantic consequence, with Kleene K3 as an instance Oct 23, 2026
@jessealama
jessealama force-pushed the kleene-propositional branch from a3d8c5a to c81f326 Compare October 23, 2026 18:10
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