The shortest possible length of the longest implicational axiom
Journal of Philosophical Logic 25 (1):101 - 108 (1996)
| Abstract | A four-valued matrix is presented which validates all theorems of the implicational fragment, IF, of the classical sentential calculus in which at most two distinct sentence letters occur. The Wajsberg/Diamond-McKinsley Theorem for IF follows as a corollary: every complete set of axioms (with substitution and detachment as rules) must include at least one containing occurrences of three or more distinct sentence letters.Additionally, the matrix validates all IF theses built from nine or fewer occurrences of connectives and letters. So the classic result of Jaskovski for the full sentential calculus —that every complete axiom set must contain either two axioms of length at least nine or else one of length at least eleven—can be improved in the implicational case: every complete axiom set for IF must contain at least one axiom eleven or more characters long. | |||||||||
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Richard Tursman (1968). The Shortest Axioms of the Implicational Calculus. Notre Dame Journal of Formal Logic 9 (4):351-358.
Tadeusz Prucnal (1974). Interpretations of Classical Implicational Sentential Calculus in Nonclassical Implicational Calculi. Studia Logica 33 (1):59 - 64.
Diderik Batens (1987). Relevant Implication and the Weak Deduction Theorem. Studia Logica 46 (3):239 - 245.
Branden Fitelson & Larry Wos (2001). Finding Missing Proofs with Automated Reasoning. Studia Logica 68 (3):329-356.
Ivo Thomas (1970). Final Word on a Shortest Implicational Axiom. Notre Dame Journal of Formal Logic 11 (1):16-16.
T. Thacher Robinson (1968). Independence of Two Nice Sets of Axioms for the Propositional Calculus. Journal of Symbolic Logic 33 (2):265-270.
Zachary Ernst, Branden Fitelson, Kenneth Harris & Larry Wos (2002). Shortest Axiomatizations of Implicational S4 and S. Notre Dame Journal of Formal Logic 43 (3):169-179.
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