English

Resolvability in c.c.c. generic extensions

General Topology 2017-02-02 v1 Logic

Abstract

Every crowded space XX is ω{\omega}-resolvable in the c.c.c generic extension VFn(X,2)V^{Fn(|X|,2}) of the ground model. We investigate what we can say about λ{\lambda}-resolvability in c.c.c-generic extensions for λ>ω{\lambda}>{\omega}? A topological space is "monotonically ω1\omega_1-resolvable" if there is a function f:Xω1f:X\to {\omega_1} such that {xX:f(x)α}denseX\{x\in X: f(x)\ge {\alpha} \}\subset^{dense}X for each α<ω1{\alpha}<{\omega_1}. We show that given a T1T_1 space XX the following statements are equivalent: (1) XX is ω1{\omega}_1-resolvable in some c.c.c-generic extension, (2) XX is monotonically ω1\omega_1-resolvable. (3) XX is ω1{\omega}_1-resolvable in the Cohen-generic extension VFn(ω1,2)V^{Fn({\omega_1},2)}. We investigate which spaces are monotonically ω1\omega_1-resolvable. We show that if a topological space XX is c.c.c, and ω1Δ(X)X<ωω{\omega}_1\le \Delta(X)\le |X|<{\omega}_{\omega}, then XX is monotonically ω1\omega_1-resolvable. On the other hand, it is also consistent, modulo the existence of a measurable cardinal, that there is a space YY with Y=Δ(Y)=ω|Y|=\Delta(Y)=\aleph_\omega which is not monotonically ω1\omega_1-resolvable. The characterization of ω1{\omega_1}-resolvability in c.c.c generic extension raises the following question: is it true that crowded spaces from the ground model are ω{\omega}-resolvable in VFn(ω,2)V^{Fn({\omega},2)}? We show that (i) if V=LV=L then every crowded c.c.c. space XX is ω{\omega}-resolvable in VFn(ω,2)V^{Fn({\omega},2)}, (ii) if there is no weakly inaccesssible cardinals, then every crowded space XX is ω{\omega}-resolvable in VFn(ω1,2)V^{Fn({\omega}_1,2)}. On the other hand, it is also consistent that there is a crowded space XX with X=Δ(X)=ω1|X|=\Delta(X)={\omega_1} such that XX remains irresolvable after adding a single Cohen real.

Keywords

Cite

@article{arxiv.1702.00326,
  title  = {Resolvability in c.c.c. generic extensions},
  author = {Lajos Soukup and Adrienne Stanley},
  journal= {arXiv preprint arXiv:1702.00326},
  year   = {2017}
}

Comments

12 pages

R2 v1 2026-06-22T18:06:50.309Z