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The truth about some Post numbers
Published online by Cambridge University Press: 12 March 2014
Extract
There is a mistake in [6], discovered by Robert V. Kohn: contrary to the claim on p. 714, the set {◊X i : i ≥ 2} is not independent in S3. As a result three problems thought to be settled are open once more, viz., whether the Post numbers of S2, S3, and K4 are denumerable. In [6] it was claimed they are not. Now we shall prove that that claim is indeed correct for S2 and K4 but, surprisingly enough, not for S3.
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- Copyright © Association for Symbolic Logic 1976
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