ArticleOriginal scientific text
Title
Strong covering without squares
Authors 1, 2
Affiliations
- Institute of Mathematics, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
- Department of Mathematics, Rutgers University, New Brunswick, NJ 08854, U.S.A.
Abstract
Let W be an inner model of ZFC. Let κ be a cardinal in V. We say that κ-covering holds between V and W iff for all X ∈ V with X ⊆ ON and V ⊨ |X| < κ, there exists Y ∈ W such that X ⊆ Y ⊆ ON and V ⊨ |Y| < κ. Strong κ-covering holds between V and W iff for every structure M ∈ V for some countable first-order language whose underlying set is some ordinal λ, and every X ∈ V with X ⊆ λ and V ⊨ |X| < κ, there is Y ∈ W such that X ⊆ Y ≺ M and V ⊨ |Y| < κ.
We prove that if κ is V-regular, , and we have both κ-covering and -covering between W and V, then strong κ-covering holds. Next we show that we can drop the assumption of -covering at the expense of assuming some more absoluteness of cardinals and cofinalities between W and V, and that we can drop the assumption that and weaken the -covering assumption at the expense of assuming some structural facts about W (the existence of certain square sequences).
Keywords
set theory, covering, strong covering lemma, pcf theory
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