Published online by Cambridge University Press: 12 March 2014
In this article, unpublished methods of Solovay and Kunen are applied to describe conditions under which an uncountable regular κ can satisfy weak (κ, λ)-compactness (see 1.1(3) below), yet lie below 2μ for some μ < κ. The argumentation is in informal ZFC, and general set-theoretic notation is standard. The lower-case Greek letters κ, λ, μ, ν are reserved for cardinals in the sense of some transitive or inner model of a reasonable set theory, φ, Ψ, θ, are (arithmetizations of) formulas in some extension of the first-order language of set theory, and other lower-case Greek letters except Є are metavariables for arbitrary ordinals. If M is transitive, M ⊨ φ abbreviates 〈M, Є 〉 ⊨ φ. [2], [3], [9] and [1] provide more information about large-cardinal theory for those who wish it.
1.1. Definitions. (1) κ is inaccessible iff κ is regular and ℵκ = κ; strongly inaccessible iff κ is regular and ℶκ = κ, i.e., λ < κ for all λ < κ; weakly inaccessible iff κ is inaccessible but not strongly inaccessible.
(2) L κλ is the infinitary language with conjunctions and disjunctions of length < κ and quantification over sequences of length < λ, and PL κ the prepositional language with κ letters and conjunctions and disjunctions of length < κ.
This is a condensed version of the second part of my thesis (Wisconsin, 1971), written under the supervision of Professor Kenneth Kunen. I would like to express again my gratitude for his friendliness, patience, infallibility and lack of possessiveness with good ideas. The most substantial one of the article is his, not mine.