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	$$⊢\phi \leftrightarrow \phi$$

Detailed syntax breakdown

Step	Hyp	Ref	Expression
0		wph	$$wff\phi$$
1	0 0	wb	$$wff\left(\phi \leftrightarrow \phi \right)$$