Theorem
pm2.49
Theorem *2.49 of [WhiteheadRussell] p. 107. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash \neg (\varphi \vee \psi) \rightarrow \neg \varphi \vee \neg \psi \)
Proof
pm2.46
olcd
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