Theorem
pm2.73
Theorem *2.73 of [WhiteheadRussell] p. 108. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash (\varphi \rightarrow \psi) \rightarrow \varphi \vee \psi \vee \chi \rightarrow \psi \vee \chi \)
Proof
pm2.621
orim1d
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