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Theorem pm5.19 361
Description: Theorem *5.19 of [WhiteheadRussell] p. 124. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm5.19  |-  -.  ( ph 
<->  -.  ph )

Proof of Theorem pm5.19
StepHypRef Expression
1 biid 239 . 2  |-  ( ph  <->  ph )
2 pm5.18 357 . 2  |-  ( (
ph 
<-> 
ph )  <->  -.  ( ph 
<->  -.  ph ) )
31, 2mpbi 211 1  |-  -.  ( ph 
<->  -.  ph )
Colors of variables: wff setvar class
Syntax hints:   -. wn 3    <-> wb 187
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 188
This theorem is referenced by:  xorexmid  1419  ru  3298  pwfseqlem1  9084  bisym1  31072  bj-ru0  31493  rusbcALT  36648
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