Theorem 3impexp

Version of impexp for a triple conjunction. (Contributed by Alan Sare, 31-Dec-2011.)

Conclusion
\( \vdash \varphi \wedge \psi \wedge \chi \rightarrow \theta \leftrightarrow \varphi \rightarrow \psi \rightarrow \chi \rightarrow \theta \)
Proof
id
l1
3expd _
id
3impd _
impbii l1 _