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Clarified title/grammar
David Roberts
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Do $X$ and $Y$ have the same cardinality if their families of finite subsets do?

Let $X$ and $Y$ be sets. It is undecidable in ZFC whether $2^{|X|} = 2^{|Y|}$ implies $|X| = |Y|$ (in Cohen's original model for ZFC + $\neg$CH, one has $2^{\aleph_0} = 2^{\aleph_1}$).

Question. Do $X$ and $Y$ have the same cardinality if the families of finite subsets of both sets do?

I feel this must be either basic or very well known (to those who know it very well).

Salvo Tringali
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