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Theorem pm4.67 417
Description: Theorem *4.67 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.67  |-  ( -.  ( -.  ph  ->  -. 
ps )  <->  ( -.  ph 
/\  ps ) )

Proof of Theorem pm4.67
StepHypRef Expression
1 pm4.63 410 1  |-  ( -.  ( -.  ph  ->  -. 
ps )  <->  ( -.  ph 
/\  ps ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    <-> wb 176    /\ wa 358
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  df-an 360
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