I recently proved the following conjecture (now a theorem):

Theorem $latex A\cap^{\mathfrak{F}}\bigcup{}^{\mathfrak{F}}S = \bigcup{}^{\mathfrak{F}} \{ A\cap^{\mathfrak{F}} X | X\in S \}$ for every set $latex A\in\mathscr{P}\mho$ and every $latex S\in\mathscr{P}\mathfrak{F}$ where $latex \mathfrak{F}$ is the set of filter objects on some set $latex \mho$.

This theorem is a direct consequence of the following lemma:

Lemma $latex A\cap^{\mathfrak{F}}$ is a lower adjoint of $latex (\mho\setminus A)\cup^{\mathfrak{F}}$ for every set $latex A\in\mathscr{P}\mho$.

Proof That $latex A\cap^{\mathfrak{F}}$ and $latex (\mho\setminus A)\cup^{\mathfrak{F}}$ are monotone is obvious.

We need to prove (for every $latex x,y\in\mathfrak{F}$) that

$latex x \subseteq (\mho\setminus A)\cup^{\mathfrak{F}}(A\cap^{\mathfrak{F}}x)$ and $latex A\cap^{\mathfrak{F}}((\mho\setminus A)\cup^{\mathfrak{F}}y) \subseteq y$.

Really, $latex (\mho \setminus A) \cup^{\mathfrak{F}} (A \cap^{\mathfrak{F}} x) =\\ ((\mho \setminus A) \cup^{\mathfrak{F}} A) \cap^{\mathfrak{F}} ((\mho\setminus A) \cup^{\mathfrak{F}} x) =\\ \mho \cap^{\mathfrak{F}} ((\mho\setminus A) \cup^{\mathfrak{F}} x) =\\ (\mho \setminus A) \cup^{\mathfrak{F}} x\supseteq x$
$latex A \cap^{\mathfrak{F}} ((\mho\setminus A)\cup^{\mathfrak{F}} y) =\\ (A \cap^{\mathfrak{F}} (\mho \setminus A))\cup^{\mathfrak{F}} (A \cap^{\mathfrak{F}} y) =\\ \emptyset \cup^{\mathfrak{F}}(A \cap^{\mathfrak{F}} y) =\\ A \cap^{\mathfrak{F}} y \subseteq y.$

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