\begin{definition}[Definition:Beta-Formula]
Let $\mathbf B$ be a WFF of propositional logic that is not a literal.
Then $\mathbf B$ is a '''$\beta$-formula''' {{iff}}:
:$\mathbf B$ is semantically equivalent to a disjunction $\mathbf B_1 \lor \mathbf B_2$
for some WFFs $\mathbf B_1, \mathbf B_2$.
\end{definition}