Theorem ninba

Miscellaneous inference relating falsehoods. (Contributed by NM, 31-Mar-1994.)

Hypothesis
ninba.1
\( \vdash \varphi \)
Conclusion
\( \vdash \neg \psi \rightarrow (\neg \varphi \leftrightarrow \chi \wedge \psi) \)
Proof
ninba.1
niabn _
bicomd _