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Theorem xchnxbi 638
Description: Replacement of a subexpression by an equivalent one. (Contributed by Wolf Lammen, 27-Sep-2014.)
Hypotheses
Ref Expression
xchnxbi.1  |-  ( -. 
ph 
<->  ps )
xchnxbi.2  |-  ( ph  <->  ch )
Assertion
Ref Expression
xchnxbi  |-  ( -. 
ch 
<->  ps )

Proof of Theorem xchnxbi
StepHypRef Expression
1 xchnxbi.2 . . 3  |-  ( ph  <->  ch )
21notbii 627 . 2  |-  ( -. 
ph 
<->  -.  ch )
3 xchnxbi.1 . 2  |-  ( -. 
ph 
<->  ps )
42, 3bitr3i 184 1  |-  ( -. 
ch 
<->  ps )
Colors of variables: wff set class
Syntax hints:   -. wn 3    <-> 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  ax-in1 577  ax-in2 578
This theorem depends on definitions:  df-bi 115
This theorem is referenced by:  xchnxbir  639
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