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Proof Mining - Mathematics, Algorithms and Proofs

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<strong>Proof</strong> <strong>Mining</strong><br />

The semi-classical case<br />

Consider the ituitionistic version BAi of BA.<br />

AC = full axiom of choice in all types<br />

CA¬ : ∃Φ∀x ρ (Φ(x) =0 0 ↔ ¬A(x)) A <strong>and</strong> ρ arbitrary.<br />

Observation: CA¬ implies WKL (<strong>and</strong> even UWKL) <strong>and</strong> the law<br />

of exluded middle for negated (<strong>and</strong> for ∃-free) formulas.<br />

Ulrich Kohlenbach 23

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