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Elementary definition

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This is an old revision of this page, as edited by AshtonBenson (talk | contribs) at 23:40, 22 November 2009 (Explain importance of "elementary" in the universe of possible definition classes). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

In mathematical logic, an elementary definition is a definition that can be made using only finitary first-order logic, and in particular without reference to set theory or using extensions such as plural quantification.

Elementary definitions are of particular interest because they admit a complete proof apparatus while still being expressive enough to support most everyday mathematics (via the addition of elementarily-expressible axioms such as ZFC).

Saying that a definition is elementary is a weaker condition than saying it is algebraic.

References

  • Mac Lane and Moerdijk, Sheaves in Geometry and Logic: A First Introduction to Topos Theory, page 4.
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