Abstract

Independence of premiss is the axiom scheme
∀x[(¬A(x) → ∃yB(x, y)) → ∃y(¬A(x) → B(x, y))]
The principle is underivable in HA, since it is inconsistent with ECT0. However,
HA is closed under the derived rule: if HA ¬A → ∃yB(y), then HA ¬A → B(n), for some natural
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