Theorem
bitr
Theorem *4.22 of [WhiteheadRussell] p. 117.
bitri
in closed form. (Contributed by NM, 3-Jan-2005.)
Conclusion
\( \vdash (\varphi \leftrightarrow \psi) \wedge (\psi \leftrightarrow \chi) \rightarrow (\varphi \leftrightarrow \chi) \)
Proof
bibi1
biimpar
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