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Theorem biid 160
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 117 1 (φφ)
Colors of variables: wff set class
Syntax hints:  wb 98
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia2 100  ax-ia3 101
This theorem depends on definitions:  df-bi 110
This theorem is referenced by:  biidd  161  3anbi1i  1094  3anbi2i  1095  3anbi3i  1096  trubitru  1303  falbifal  1306  eqid  2037  abid2  2155  abid2f  2199  ceqsexg  2666
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