The Morris model
Logic
2020-10-05 v3
Abstract
Douglass B. Morris announced in 1970 that it is consistent with ZF that "For every , there exists a set which is the countable union of countable sets, and can be partitioned into non-empty sets". The result was never published in a journal (it was proved in full in Morris' dissertation) and seems to have been lost, save a mention in Jech's "Axiom of Choice". We provide a proof using modern tools derived from recent work of the author. We also prove a new preservation theorem for general products of symmetric systems, which we use to obtain the consistency of Dependent Choice with the above statement (replacing "countable union of countable sets" by "union of sets of size ").
Keywords
Cite
@article{arxiv.1811.10977,
title = {The Morris model},
author = {Asaf Karagila},
journal= {arXiv preprint arXiv:1811.10977},
year = {2020}
}
Comments
12 pages (11+references)