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Difference between revisions of "Inconsistent class"

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A class <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504901.png" /> of formulas in the language of a given formal theory having the property that there is a formula <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504902.png" /> such that both <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504903.png" /> and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504904.png" /> (the negation of <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504905.png" />) can be deduced from <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504906.png" /> in this theory. In other words, if all formulas in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504907.png" /> are added to the axioms of the theory as new axioms, then in the theory obtained one can deduce both the formula <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504908.png" /> and the formula <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/i/i050/i050490/i0504909.png" />.
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A class $K$ of formulas in the language of a given formal theory having the property that there is a formula $\phi$ such that both $\phi$ and $\neg\phi$ (the negation of $\phi$) can be deduced from $K$ in this theory. In other words, if all formulas in $K$ are added to the axioms of the theory as new axioms, then in the theory obtained one can deduce both the formula $\phi$ and the formula $\neg\phi$.
  
  

Latest revision as of 15:40, 9 April 2014

A class $K$ of formulas in the language of a given formal theory having the property that there is a formula $\phi$ such that both $\phi$ and $\neg\phi$ (the negation of $\phi$) can be deduced from $K$ in this theory. In other words, if all formulas in $K$ are added to the axioms of the theory as new axioms, then in the theory obtained one can deduce both the formula $\phi$ and the formula $\neg\phi$.


Comments

References

[a1] A. Grzegorczyk, "An outline of mathematical logic" , Reidel (1974)
[a2] S.C. Kleene, "Introduction to metamathematics" , North-Holland & Noordhoff (1950) pp. Chapt. XIV
How to Cite This Entry:
Inconsistent class. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Inconsistent_class&oldid=31460
This article was adapted from an original article by V.N. Grishin (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article