Definition:Beta-Formula

Definition
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 $\mathbf B_1, \mathbf B_2$.