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Models with second order properties in successors of singulars

Published online by Cambridge University Press:  12 March 2014

Rami Grossberg*
Affiliation:
Department of Mathematics, Rutgers University, New Brunswick, New Jersey 08903
*
Department of Mathematics, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213

Abstract

Let L(Q) be first order logic with Keisler's quantifier, in the λ+ interpretation (= the satisfaction is defined as follows: M ⊨ (Qx)φ(x) means there are λ+ many elements in M satisfying the formula φ(x)).

Theorem 1. Let λ be a singular cardinal; assume λ and GCH. If T is a complete theory in L(Q) of cardinality at most λ, and p is an L(Q) 1-type so that T strongly omits p( = p has no support, to be defined in §1), then T has a model of cardinality λ+ in the λ+ interpretation which omits p.

Theorem 2. Let λ be a singular cardinal, and let T be a complete first order theory of cardinality λ at most. Assume □λ and GCH. If Γ is a smallness notion then T has a model of cardinality λ+ such that a formula φ(x) is realized by λ+ elements of M iff φ(x) is not Γ-small. The theorem is proved also when λ is regular assuming λ = λ. It is new when λ is singular or when ∣T∣ = λ is regular.

Theorem 3. Let λ be singular. If Con(ZFC + GCH + ∃κ) [κ is a strongly compact cardinal]), then the following is consistent: ZFC + GCH + the conclusions of all above theorems are false.

Type
Research Article
Copyright
Copyright © Association for Symbolic Logic 1989

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