Rule of Addition/Proof Rule/Tableau Form

Proof Rule
Let $\phi$ and $\psi$ be two propositional formulas.

The Rule of Addition is invoked in a tableau proof for $\phi$ or $\psi$ in either of the two forms:


 * Form 1:

Let $\phi$ be a propositional formula in a tableau proof.


 * Form 2:

Let $\psi$ be a propositional formula in a tableau proof.