# Proper Filter is Included in Ultrafilter in Boolean Lattice

## Theorem

Let $L = \left({S, \vee, \wedge, \preceq}\right)$ be a Boolean lattice.

Let $F$ be a proper filter on $L$.

Then there exists ultrafilter $G$ on $L$: $F \subseteq G$

## Proof

$I := \left\{ {\bot}\right\}$ is an ideal in $L$.

where $\bot$ denotes the bottom of $L$.

We will prove that

$F \cap I = \varnothing$

Let $x \in I$.

By definition of singleton:

$x = \bot$

Thus by Bottom not in Proper Filter:

$x \notin F$

$\Box$

there exists a prime filter $G$ on $L$: $F \subseteq G$ and $G \cap I = \varnothing$

By definition of singleton:

$\bot \in I$

By definitions of empty set and intersection:

$\bot \notin G$
$G$ is proper.
$G$ is ultrafilter.

Thus $F \subseteq G$

$\blacksquare$