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math.LO2023
A Shelah group in ZFC
Márk Poór, Assaf Rinot
In a paper from 1980, Shelah constructed an uncountable group all of whose proper subgroups are countable. Assuming the continuum hypothesis, he constructed an uncountable group $G…
math.LO2023
On the weak Borel chromatic number and cardinal invariants of the continuum
Márk Poór, Saharon Shelah
We prove that consistently, cov(, where denotes the weak Borel chromatic number of the…