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Published online by Cambridge University Press: 02 May 2022
In this paper we build an Asperó–Mota iteration of length $\omega _2$ that adds a family of $\aleph _2$ many club subsets of $\omega _1$ which cannot be diagonalized while preserving $\aleph _2$. This result discloses a technical limitation of some types of Asperó–Mota iterations.
The author is supported by Grant-in-Aid for Scientific Research (C) 18K03393, Japan Society for the Promotion of Science.