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Asaf Karagila
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Constructing a section of an equivalence relation compatible with the intersection

Let $X$ be a (countably) infinite set and define an equivalence relation $\sim$ on the power set $P(X)$ of $X$ by defining two subsets $A$ and $B$ of $X$ to be equivalent if they differ by at most finitely many elements (i.e., $A \sim B$ if the symmetric difference $A \Delta B$ is finite).

Let $[-]\colon P(X) \to P(X)/_{\sim}$ denote the quotient map onto the equivalence classes. Does there exist a section $s \colon P(X)/_{\sim} \to P(X)$ of it with the following three properties?

  1. $s([\emptyset]) = \emptyset$.
  2. $s([X]) = X$.
  3. For every $A$ and $B$ in $P(X)$ we have $s([A]) \cap s([B]) = s([A \cap B])$.

I tried around constructing such a section by using the Lemma of Zorn, but I couldn't figure out how to make the crucial step in the argument work (enlarging the domain of such a section, but which is defined only on a subset of $P(X)/_{\sim}$, by at least one more missing element from $P(X)/_{\sim}$).