Metamath Proof Explorer


Axiom ax-frege54a

Description: Reflexive equality of wffs. The content of ph is identical with the content of ph . Part of Axiom 54 of Frege1879 p. 50. Identical to biid . (Contributed by RP, 24-Dec-2019) (New usage is discouraged.)

Ref Expression
Assertion ax-frege54a
|- ( ph <-> ph )

Detailed syntax breakdown

Step Hyp Ref Expression
0 wph
 |-  ph
1 0 0 wb
 |-  ( ph <-> ph )