Theorem
pm3.11
Theorem *3.11 of [WhiteheadRussell] p. 111. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash \neg (\neg \varphi \vee \neg \psi) \rightarrow \varphi \wedge \psi \)
Proof
anor
biimpri
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