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Theorem biid 164
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 121 1 (𝜑𝜑)
Colors of variables: wff set class
Syntax hints:  wb 102
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia2 104  ax-ia3 105
This theorem depends on definitions:  df-bi 114
This theorem is referenced by:  biidd  165  3anbi1i  1106  3anbi2i  1107  3anbi3i  1108  trubitru  1322  falbifal  1325  eqid  2056  abid2  2174  abid2f  2218  ceqsexg  2694  nnwetri  6384
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