Metamath Proof Explorer

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 
|- ( ( ph <-> ps ) -> ( ps <-> ph ) )

Proof

Step Hyp Ref Expression
1 bicom1 
 |-  ( ( ph <-> ps ) -> ( ps <-> ph ) )