Some remarks on a question of D. H. Fremlin regarding epsilon-density

Citation
Aw. Apter et M. Dzamonja, Some remarks on a question of D. H. Fremlin regarding epsilon-density, ARCH MATH L, 40(7), 2001, pp. 531-540
Citations number
11
Categorie Soggetti
Mathematics
Journal title
ARCHIVE FOR MATHEMATICAL LOGIC
ISSN journal
09335846 → ACNP
Volume
40
Issue
7
Year of publication
2001
Pages
531 - 540
Database
ISI
SICI code
0933-5846(200110)40:7<531:SROAQO>2.0.ZU;2-H
Abstract
We show the relative consistency of N-1 satisfying a combinatorial property considered by David Fremlin (in the question DU from his list) in certain choiceless inner models. This is demonstrated by first proving the property is true for Ramsey cardinals. In contrast, we show that in ZFC, no cardina l of uncountable cofinality can satisfy a similar, stronger property. The q uestions considered by D. H. Fremlin are if families of finite subsets of o mega (1) satisfying a certain density condition necessarily contain all fin ite subsets of an infinite subset of omega (1), and specifically if this an d a stronger property hold under MA + -CH. Towards this we show that if MA + -CH holds. then for every family. A of N-1 many infinite subsets of omega (1) one can find a family L of finite subsets of omega (1) which is dense in Fremlin's sense, and does not contain all finite subsets of any set in A . We then pose some open problems related to the question.