Dual of Dual Statement (Order Theory)
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Theorem
Let $\Sigma$ be a statement about ordered sets.
Let $\Sigma^*$ be its dual statement.
Then $\Sigma$ is also the dual statement of $\Sigma^*$.
Proof
By definition, the dual statement $\Sigma^*$ is formed by replacing the ordering $\preceq$ with its dual $\succeq$.
By Dual of Dual Ordering, applying this operation twice results in the original sentence $\Sigma$ again.
$\blacksquare$