Contents Online
Mathematical Research Letters
Volume 5 (1998)
Number 2
A dichotomy for forcing notions
Pages: 213 – 226
DOI: https://dx.doi.org/10.4310/MRL.1998.v5.n2.a8
Author
Abstract
Let $B$ be Baumgartner’s poset for adding a closed unbounded subset of $\omega_1$ with finite conditions. Under the Proper Forcing Axiom, a forcing notion $P$ of size $\aleph_1$ is nowhere c.c.c. if and only if $B$ completely embeds into $P.$
Published 1 January 1998