Finished Propositional Tableau has Finished Branch or is Confutation

Theorem
Let $\struct {T, \mathbf H, \Phi}$ be a finished propositional tableau.

Then one of the following holds:


 * $T$ has a finished branch
 * $T$ is a tableau confutation.

Proof
Suppose $T$ has no finished branch.

Then since $T$ is finished, every branch of $T$ is contradictory.

Hence $T$ is a tableau confutation.