Theorem frege55aid

Description: Lemma for frege57aid . Core proof of Proposition 55 of Frege1879 p. 50. (Contributed by RP, 24-Dec-2019)

	Ref	Expression
Assertion	frege55aid	$$⊢\left(\phi \leftrightarrow \psi \right)\to \left(\psi \leftrightarrow \phi \right)$$

Proof

Step	Hyp	Ref	Expression
1		bicom1	$$⊢\left(\phi \leftrightarrow \psi \right)\to \left(\psi \leftrightarrow \phi \right)$$