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Theorem pm5.501 242
Description: Theorem *5.501 of [WhiteheadRussell] p. 125. (Contributed by NM, 3-Jan-2005.) (Revised by NM, 24-Jan-2013.)
Assertion
Ref Expression
pm5.501  |-  ( ph  ->  ( ps  <->  ( ph  <->  ps ) ) )

Proof of Theorem pm5.501
StepHypRef Expression
1 pm5.1im 171 . 2  |-  ( ph  ->  ( ps  ->  ( ph 
<->  ps ) ) )
2 bi1 116 . . 3  |-  ( (
ph 
<->  ps )  ->  ( ph  ->  ps ) )
32com12 30 . 2  |-  ( ph  ->  ( ( ph  <->  ps )  ->  ps ) )
41, 3impbid 127 1  |-  ( ph  ->  ( ps  <->  ( ph  <->  ps ) ) )
Colors of variables: wff set class
Syntax hints:    -> wi 4    <-> wb 103
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106
This theorem depends on definitions:  df-bi 115
This theorem is referenced by:  ibib  243  ibibr  244  pm5.1  566  pm5.18dc  811  biassdc  1327
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