More on the revised GCH and the black box

Saharon Shelah*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

We strengthen the revised GCH theorem by showing, e.g., that for λ=cf(λ) >]ω for all but finitely many regular k<]ω it holds that " λ is accessible on cofinality k" in some weak sense (see below). As a corollary, λ=2μ+>]ω implies that the diamond holds on λ when restricted to cofinality k for all but finitely many k ∈ Reg ∩ ]ω We strengthen previous results on the black box and the middle diamond: previously it was established that these principles hold on { δ:δ<λ, cf (δ)=(] n )+ } for sufficiently large n; here we succeed in replacing a sufficiently large ] n with a sufficiently large א n. The main theorem, concerning the accessibility of λ on cofinality K , Theorem 3.1, implies as a special case that for every regular λ > ] ω , for some K <] ω , we can find a sequence (P δ : δ < λ) such that u ∈ P δ ⇒ u = δ &Engl | u | < ] ω , | Pδ | < λ, and we can fix a finite set d of "exceptional" regular cardinals θ < ] ω so that if A ⊂λ satisfies | A | < ]ω , there is a pair-coloring c : [ A ]2 → k so that for every c-monochromatic B ∈ A with no last element, letting λ : = sup B it holds that B ∈ Pδ - provided that θ : = cf ( λ ) is not one of the finitely many "exceptional" members of d.

Original languageEnglish
Pages (from-to)133-160
Number of pages28
JournalAnnals of Pure and Applied Logic
Volume140
Issue number1-3
DOIs
StatePublished - Jul 2006

Keywords

  • Black box
  • Middle diamond
  • Revised GCH

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