Biconditional Elimination/Proof Rule/Tableau Form

Proof Rule
Let $\phi \iff \psi$ be a propositional formula] in a tableau proof whose main connective is the biconditional operator.

Biconditional Elimination is invoked for $\phi \iff \psi$ in either of the two forms:


 * Form 1:


 * Form 2:

Also denoted as
Sources which refer to this rule as the biconditional-conditional rule may as a consequence give the abbreviation $\mathrm {BC}$.