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Theorem pm4.8 656
Description: Theorem *4.8 of [WhiteheadRussell] p. 122. This one holds for all propositions, but compare with pm4.81dc 850 which requires a decidability condition. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.8  |-  ( (
ph  ->  -.  ph )  <->  -.  ph )

Proof of Theorem pm4.8
StepHypRef Expression
1 pm2.01 579 . 2  |-  ( (
ph  ->  -.  ph )  ->  -.  ph )
2 ax-1 5 . 2  |-  ( -. 
ph  ->  ( ph  ->  -. 
ph ) )
31, 2impbii 124 1  |-  ( (
ph  ->  -.  ph )  <->  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    <-> wb 103
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia2 105  ax-ia3 106  ax-in1 577
This theorem depends on definitions:  df-bi 115
This theorem is referenced by: (None)
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