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The occurrence of an implication in finitely valid, intuitively improvable formulas of propositional logic
D. P. Skvortsov M. V. Lomonosov Moscow State University
Abstract:
Kabakov has proved that for the finite validity (in Medvedev's sense) of intuitively unprovable propositional formulas it is necessary that an implication occur in the premise $\beta$ or else in the inference $\gamma$ of some subformula of the type $(\beta\to\gamma)$, and, consequently, that at least two implications be present. Here we prove that every finitely valid, intuitively unprovable formula contains the occurrence of an implication necessarily in the premise $\beta$ of some subformula of the form $(\beta\to\gamma)$ and we also present an example of a similar formula containing exactly two implications.
Received: 20.05.1974
Citation:
D. P. Skvortsov, “The occurrence of an implication in finitely valid, intuitively improvable formulas of propositional logic”, Mat. Zametki, 20:3 (1976), 383–390; Math. Notes, 20:3 (1976), 771–775
Linking options:
https://www.mathnet.ru/eng/mzm7857 https://www.mathnet.ru/eng/mzm/v20/i3/p383
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