Theorem
pm5.5
Theorem *5.5 of [WhiteheadRussell] p. 125. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash \varphi \rightarrow (\varphi \rightarrow \psi \leftrightarrow \psi) \)
Proof
biimt
bicomd
_
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