On needed reals
Heike Mildenberger, Saharon Shelah
Abstract
Following Blass, we call a real a ``needed'' for a binary relation R on the reals if in every R-adequate set we find an element from which a is Turing computable. We show that every real needed for Cof(N) is hyperarithmetic. Replacing ``R-adequate'' by ``R-adequate with minimal cardinality'' we get related notion of being ``weakly needed''. We show that is is consistent that the two notions do not coincide for the reaping relation. (They coincide in many models.) We show that not all hyperarithmetical reals are needed for the reaping relation. This answers some questions asked by Blass at the Oberwolfach conference in December 1999.
Create a lesson
Related papers
Pseudofinite abelian groups and asymptotic classes of finite abelian groups
Carlos Cordoba-Caycedo, Dario Garcia
Spectral Theory and Descriptive Combinatorics for Non-Regular Borel pmp Graphs
Cecelia Higgins, Pieter Spaas, Sofia Torelli
The strength of the minimum principle in constructive reverse mathematics
Tatsuji Kawai
Independence of premise for intuitionistic Zermelo-Fraenkel set theory
Patrick Uftring
Condensed Whitehead Problem
Spencer Unger, Jerry Wei
Points and their multiples on curves in powers of simple abelian varieties
David J. Smith