Are all atoms of the lattice of filters (ordered by set-theoretic inclusion) principal filters?
Note that atoms of this lattice are not ultrafilters (ultrafilters are atoms of the dual lattice).
Are all atoms of the lattice of filters (ordered by set-theoretic inclusion) principal filters?
Note that atoms of this lattice are not ultrafilters (ultrafilters are atoms of the dual lattice).
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The answer is yes.
Suppose a non-principal filter $F$ on a set $U$ is an atom. Then there exists a set $M\ne U$ such that $M\in F$. Consider an element $x\in U$ such that $x\notin M$. Then the principal filter corresponding to the set $U\setminus\{x\}$ is strictly above $F$. So $F$ is not an atom.