Theorem biid 169

Description: Principle of identity for logical equivalence. Theorem *4.2 of [WhiteheadRussell] p. 117. (Contributed by NM, 5-Aug-1993.)

Assertion

Ref	Expression
biid	|- ( ph <-> ph )

Proof of Theorem biid

Step	Hyp	Ref	Expression
1		id 19	. 2 |- ( ph -> ph )
2	1, 1	impbii 124	1 |- ( ph <-> ph )

Syntax hints:   <-> wb 103

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia2 105  ax-ia3 106

This theorem depends on definitions:  df-bi 115

This theorem is referenced by:  biidd  170  3anbi1i  1134  3anbi2i  1135  3anbi3i  1136  trubitru  1351  falbifal  1354  eqid  2088  abid2  2208  abid2f  2253  ceqsexg  2743  nnwetri  6606  fsum2d  10792