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Theorem bj-currypara 34009
Description: Curry's paradox. Note that the proof is intuitionistic (use ax-3 8 comes from the unusual definition of the biconditional in The paradox comes from the case where 𝜑 is the self-referential sentence "If this sentence is true, then 𝜓", so that one can prove everything. Therefore, a consistent system cannot allow the formation of such self-referential sentences. This has lead to the study of logics rejecting contraction pm2.43 56, such as affine logic and linear logic. (Contributed by BJ, 23-Sep-2023.)
Ref Expression
bj-currypara ((𝜑 ↔ (𝜑𝜓)) → 𝜓)

Proof of Theorem bj-currypara
StepHypRef Expression
1 bj-animbi 34008 . 2 ((𝜑𝜓) ↔ (𝜑 ↔ (𝜑𝜓)))
2 simpr 488 . 2 ((𝜑𝜓) → 𝜓)
31, 2sylbir 238 1 ((𝜑 ↔ (𝜑𝜓)) → 𝜓)
Colors of variables: wff setvar class
Syntax hints:  wi 4  wb 209  wa 399
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 210  df-an 400
This theorem is referenced by: (None)
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