Theorem norbi

If neither of two propositions is true, then these propositions are equivalent. (Contributed by BJ, 26-Apr-2019.)

Conclusion
\( \vdash \neg (\varphi \vee \psi) \rightarrow (\varphi \leftrightarrow \psi) \)
Proof
l0
orc
olc
pm5.21ni l0 _