Theorem
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Theorem 19.18 of [Margaris] p. 90. (Contributed by NM, 12-Mar-1993.)
Conclusion
\( \vdash \forall x \, (\varphi \leftrightarrow \psi) \rightarrow (\exists x \, \varphi \leftrightarrow \exists x \, \psi) \)
Proof
id
alexbii
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