Theorem biid 170

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 125	1 |- ( ph <-> ph )

Syntax hints:   <-> wb 104

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia2 106  ax-ia3 107

This theorem depends on definitions:  df-bi 116

This theorem is referenced by:  biidd  171  3anbi1i  1172  3anbi2i  1173  3anbi3i  1174  trubitru  1393  falbifal  1396  eqid  2137  abid2  2258  abid2f  2304  ceqsexg  2808  nnwetri  6797  fsum2d  11197  isstructim  11962