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Project-declaredLean 4.32.1 Β· mathlib@520045ab

Unprovable flon

LO.FirstOrder.ProvabilityAbstraction.unprovable_flon

Project documentation

Formalized law of noncontradiction cannot be proved. Alternative formulation of GΓΆdel's second incompleteness theorem.

Exact Lean statement

lemma unprovable_flon [consis : Consistent T] [𝔅.FormalizedCompleteOn 𝐉] : T ⊬ flon 𝔅 π”š

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Full Lean sourceLean 4
lemma unprovable_flon [consis : Consistent T] [𝔅.FormalizedCompleteOn 𝐉] : T ⊬ flon 𝔅 π”š := by  contrapose! consis;  replace consis : T ⊒ βˆ€ΒΉ safe 𝔅 π”š := by simpa [flon] using consis;  have h₁ : T ⊒ ∼(𝔅 𝐉 ⋏ π”š 𝐉) := by simpa [safe] using! FirstOrder.Theory.Proof.specialize _ _ ⨀ consis;  have hβ‚‚ : T ⊒ βˆΌπ‰ := (contra! jeroslow_not_safe) ⨀ h₁;  have h₃ : T ⊒ 𝐉 👘 π”š 𝐉 := jeroslow_def';  have hβ‚„ : T ⊒ π”š 𝐉 := R1' hβ‚‚;  have hβ‚… : T ⊒ π”š 𝐉 πŸ‘’ 𝐉 := by cl_prover [h₃];  have h₆ : T ⊒ 𝐉 := hβ‚… ⨀ hβ‚„;  exact not_consistent_iff_inconsistent.mpr <| inconsistent_iff_provable_bot.mpr $ (N!_iff_CO!.mp hβ‚‚) ⨀ h₆;
Project
Foundation
License
Apache-2.0
Commit
8dcdb3196454
Source
Foundation/FirstOrder/Incompleteness/ProvabilityAbstraction/Refutability.lean:116-125

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