Theorem
pm5.36
Theorem *5.36 of [WhiteheadRussell] p. 125. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash \varphi \wedge (\varphi \leftrightarrow \psi) \leftrightarrow \psi \wedge (\varphi \leftrightarrow \psi) \)
Proof
id
pm5.32ri
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