Let be a set, and let be an ultrafilter on , let be a formula of a given language , and let be any collection of structures which is indexed by the set . Denote by the equivalence class of under , for any element of the product . Then the ultraproduct satisfies via a valuation in ,
Łoś' Theorem
See also
Nonstandard Analysis, Structure, Transfer PrincipleThis entry contributed by Matt Insall (author's link)
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References
Bell, J. L. and Slomson, A. B. Models and Ultraproducts: an Introduction. Amsterdam, Netherlands: North-Holland, 1971.Hurd, A. E. and Loeb, P. A. An Introduction to Nonstandard Real Analysis. Orlando, FL: Academic Press, 1985.Referenced on Wolfram|Alpha
Łoś' TheoremCite this as:
Insall, Matt. "Łoś' Theorem." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/LosTheorem.html