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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 (𝜑𝜑)

Proof of Theorem biid
StepHypRef Expression
1 id 19 . 2 (𝜑𝜑)
21, 1impbii 125 1 (𝜑𝜑)
Colors of variables: wff set class
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  1155  3anbi2i  1156  3anbi3i  1157  trubitru  1376  falbifal  1379  eqid  2115  abid2  2236  abid2f  2281  ceqsexg  2785  nnwetri  6770  fsum2d  11155  isstructim  11879
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