Theorem pm5.1

Two propositions are equivalent if they are both true. Theorem *5.1 of [WhiteheadRussell] p. 123. (Contributed by NM, 21-May-1994.)

Conclusion
\( \vdash \varphi \wedge \psi \rightarrow (\varphi \leftrightarrow \psi) \)
Proof
pm5.501
biimpa _