1. Making the hyperreal line both saturated and complete
- Author
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H. Jerome Keisler and James H. Schmerl
- Subjects
Combinatorics ,Philosophy ,Logic ,Second-order arithmetic ,Bounded function ,Calculus ,Hyperreal number ,Uncountable set ,Finite intersection property ,Cofinality ,Upper and lower bounds ,Mathematics ,Ordered field - Abstract
In a nonstandard universe, the κ-saturation property states that any family of fewer than κ internal sets with the finite intersection property has a nonempty intersection. An ordered field F is said to have the λ-Bolzano-Weierstrass property iff F has cofinality λ and every bounded λ-sequence in F has a convergent λ-subsequence. We show that if κ < λ are uncountable regular cardinals and βα < λ whenever α < κ and β < λ then there is a κ-saturated nonstandard universe in which the hyperreal numbers have the λ-Bolzano-Weierstrass property. The result also applies to certain fragments of set theory and second order arithmetic.
- Published
- 1991
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