Theorem
pm2.42
Theorem *2.42 of [WhiteheadRussell] p. 106. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash \neg \varphi \vee (\varphi \rightarrow \psi) \rightarrow \varphi \rightarrow \psi \)
Proof
l0
pm2.21
id
jaoi
l0
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