Łoś 1955: ultraproduct of structures satisfies sentence iff ultrafilter-many factors do. Constructs nonstandard-models / hyperreals (Robinson 1966 nonstandard analysis).
Łoś 1955: ultraproduct of structures satisfies sentence iff ultrafilter-many factors do. Constructs nonstandard-models / hyperreals (Robinson 1966 nonstandard analysis).