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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
StepHypRef Expression
1 id 19 . 2  |-  ( ph  ->  ph )
21, 1impbii 124 1  |-  ( ph  <->  ph )
Colors of variables: wff set class
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  1130  3anbi2i  1131  3anbi3i  1132  trubitru  1347  falbifal  1350  eqid  2083  abid2  2203  abid2f  2247  ceqsexg  2733  nnwetri  6551
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