9
$\begingroup$

In a previous question, I asked about the impact of strong chains in $^{\omega_1}\omega_1$ (e.g., sequences of functions $\langle f_\alpha:\alpha<\kappa\rangle$ in $^{\omega_1}\omega_1$ that are strictly increasing modulo the ideal of finite sets) on cardinal characteristics of the continuum.

Koszmider [1] proved it is consistent that there is a strong chain in $^{\omega_1}{\omega_1}$ of length $\omega_2$, and Veličković and Venturi showed that Neeman's techniques (finite approximations with side conditions consisting of elementary submodels of two types) can be adapted to obtain the same result. Certainly this latter proof does not adapt in a straightforward manner to yield chains of even longer length. I am less familiar with Koszmider's original proof, but that seems to work only for $\omega_2$ as well.

Question: Is it consistent that there is a sequence $\langle f_\alpha:\alpha<\omega_3\rangle$ in $^{\omega_1}\omega_1$ that is increasing modulo the ideal of finite sets? What is known about this?

[1] Koszmider, Piotr, On strong chains of uncountable functions, Isr. J. Math. 118, 289-315 (2000). ZBL0961.03039.

[2] Veličković, Boban; Venturi, Giorgio, Proper forcing remastered, Cummings, James (ed.) et al., Appalachian set theory 2006–2012. Based on the Appalachian set theory workshop series during the period 2006–2012. Cambridge: Cambridge University Press (ISBN 978-1-107-60850-4/pbk). London Mathematical Society Lecture Note Series 406, 331-362 (2013). ZBL1367.03094.

$\endgroup$
2
  • 2
    $\begingroup$ I had asked Boban about this question and I think it is still open. I like this problem very much and it is really interesting. It can serve as a test question for finding the method of size conditions with finite conditions which can add objects of size $\aleph_3$. I don't remember if Boban has mentioned any result around this problem to me. I will ask him in the next online meeting! $\endgroup$
    – Rahman. M
    Commented Mar 22, 2020 at 10:10
  • 2
    $\begingroup$ @Rahman.M I'm still trying to map out what is known and unknown, so I should have more questions on here soon. Shelah has some ZFC limits on what can happen larger cardinals. $\endgroup$ Commented Mar 22, 2020 at 15:35

0

You must log in to answer this question.

Browse other questions tagged .