Theorem
pm5.11
Theorem *5.11 of [WhiteheadRussell] p. 123. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash (\varphi \rightarrow \psi) \vee (\neg \varphi \rightarrow \psi) \)
Proof
pm5.11g
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