Implicative propositional calculus

A propositional calculus using only the primitive connective $ \supset $( implication). Examples of an implicative propositional calculus are the complete (or classical) implicative propositional calculus given by the axioms

$$ p \supset ( q \supset p ) ,\ \ ( ( p \supset q ) \supset \ ( ( q \supset r ) \supset \ ( p \supset r ) ) ) , $$

$$ ( ( p \supset q ) \supset p ) \supset p $$

and the rules of inference: modus ponens and substitution; another example is the positive implicative propositional calculus given by the axioms

$$ p \supset ( q \supset p ) ,\ \ ( p \supset ( q \supset r ) ) \supset \ ( ( p \supset q ) \supset \ ( p \supset r ) ) $$

and the same rules of inference. Every implicative formula, that is, a formula only containing the connective $ \supset $, is deducible in complete (or positive) implicative propositional calculus if and only if it is deducible in classical (respectively, intuitionistic) propositional calculus. For any finite set $ V $ of variables, among the formulas with variables in $ V $ there is only a finite number of pairwise inequivalent ones in the positive implicative propositional calculus (see [3]). There exist undecidable finitely-axiomatizable implicative propositional calculi (see [4]).

#### References[edit]

[1] |  A. Church, "Introduction to mathematical logic" , 1 , Princeton Univ. Press (1956)

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[2] |  J. Łukasiewicz, A. Tarski, "Untersuchungen über den Aussagenkalkül" C.R. Soc. Sci. Letters Varsovie, Cl. III , 23 (1930) pp. 30–50
[3] |  A. Diego, "Sur les algèbres de Hilbert" , Gauthier-Villars (1966) ((translated from the Spanish))
[4] |  M.D. Gladstone, "Some ways of constructing a propositional calculus of any required degree of unsolvability" Trans. Amer. Math. Soc. , 118 (1965) pp. 192–210