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Paper IPM / Computer Science / 10872 |
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Abstract: | |
It is shown that the intuitionistic theory of polynomial induction on positive ?1b (coNP) formulas does not prove the sentence ��?x, yz = y(x = - y - ? x = - z - ). This implies the unprovability of the scheme ��PIND(S1b+) in the mentioned theory. However, this theory contains the sentence ?x, y��z = y(x = - y - ? x = - z - ). The above independence result is proved by constructing an ?-chain of submodels of a countable model of S2 + O3 + �exp such that none of the worlds in the chain satisfies the sentence, and interpreting the chain as a Kripke model.
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