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Logical consequence

From Encyclopedia of Mathematics
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of a given set of premises

A proposition that is true for any interpretation of the non-logical symbols (that is, the names (cf. Name) of objects, functions, predicates) for which the premises are true. If a proposition $A$ is a logical consequence of a set of propositions $\Gamma$, one says that $\Gamma$ logically implies $A$, or that $A$ follows logically from $\Gamma$.

If $\Gamma$ is a set of statements of a formalized first-order logico-mathematical language (cf. Logico-mathematical calculus) and $A$ is a proposition of this language, then the relation "A is a logical consequence of G" means that any model for $\Gamma$ is a model for $A$. This relation is denoted by $\Gamma\vDash A$. The Gödel completeness theorem of classical predicate calculus implies that the relation $\Gamma\vDash A$ coincides with the relation $\Gamma\vdash A$, that is, $\Gamma\vDash A$ if and only if $A$ is deducible from $\Gamma$ by the methods of classical predicate calculus.

References

[1] H. Rasiowa, "The mathematics of metamathematics" , Polska Akad. Nauk (1963)
[2] K. Gödel, "Die Vollständigkeit der Axiome des logischen Funktionenkalküls" Monatsh. Math. Phys. , 37 (1930) pp. 349–360


Comments

The phrase "semantic entailment" is sometimes used instead of "logical consequence" ; thus, the expression $\Gamma\vDash A$ is read as "G semantically entails A" . The expression $\Gamma\vdash A$ is similarly read as "G syntactically entails A" .

References

[a1] P.T. Johnstone, "Notes on logic and set theory" , Cambridge Univ. Press (1987)
[a2] A. Grzegorczyk, "An outline of mathematical logic" , Reidel (1974)
How to Cite This Entry:
Logical consequence. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Logical_consequence&oldid=31698
This article was adapted from an original article by V.E. Plisko (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article