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Theorem pm5.19 349
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 227 . 2  |-  ( ph  <->  ph )
2 pm5.18 345 . 2  |-  ( (
ph 
<-> 
ph )  <->  -.  ( ph 
<->  -.  ph ) )
31, 2mpbi 199 1  |-  -.  ( ph 
<->  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    <-> wb 176
This theorem is referenced by:  ru  2990  pwfseqlem1  8280  bisym1  24858  rusbcALT  27639  compneOLD  27643
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
This theorem depends on definitions:  df-bi 177
  Copyright terms: Public domain W3C validator