Soundness and Completeness of Semantic Tableaus/Corollary 1

Corollary to Soundness and Completeness of Semantic Tableaus
Let $\mathbf A$ be a WFF of propositional logic.

Let $T$ be a completed semantic tableau for $\mathbf A$.

Then $\mathbf A$ is satisfiable $T$ is open.

Proof
$\mathbf A$ is satisfiable it is not unsatisfiable.

By the Soundness and Completeness of Semantic Tableaus, $\mathbf A$ is satisfiable $T$ is not closed.

Since $T$ is completed, this is the case $T$ is open.