Theorem pm2.5g

General instance of Theorem *2.5 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Wolf Lammen, 9-Oct-2012.)

Conclusion

\( \vdash \neg (\varphi \rightarrow \psi) \rightarrow \neg \varphi \rightarrow \chi \)

Proof

simplim

pm2.24d _