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An Elementary Definability Theorem for First Order Logic  (Make Corrections)  
C. Butz, I. Moerdijk



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Abstract: this paper, we will present a definability theorem for first order logic. This theorem is very easy to state, and its proof only uses elementary tools. To explain the theorem, let us first observe that if M is a model of a theory T in a language L, then, clearly, any definable subset S ae M (i.e., a subset S = fa j M j= '(a)g defined by some formula ') is invariant under all automorphisms of M . The same is of course true for subsets of M (Update)

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BibTeX entry:   (Update)

@misc{ butz-elementary,
  author = "C. Butz and I. Moerdijk",
  title = "An Elementary Definability Theorem for First Order Logic",
  url = "citeseer.ist.psu.edu/206399.html" }
Citations (may not include all citations):
133   Cambridge University Press (context) - Hodges - 1993
83   Sheaves in Geometry and Logic (context) - Lane, Moerdijk - 1992
22   On Padoa's method in the theory of definition (context) - Beth - 1953
11   Logic with denumerably long formulas and finite strings of q.. (context) - Scott - 1965
4   Classifying toposes for first order theories - Butz, Johnstone - 1997
2   Representing topoi by topological groupoids - Butz, Moerdijk - 1996
2   Constructive sheaf semantics (context) - Palmgren - 1997
1   All topoi are localic or why permutation models prevail (context) - Freyd - 1987
1   Booleschewertige Logik (context) - Koppelberg - 1985
1   and semantics of infinitary languages (context) - Kueker, automorphisms et al. - 1968

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