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Theorem nnelOLD 2749
Description: Obsolete proof of nnel 2748 as of 25-Nov-2019. (Contributed by Alexander van der Vekens, 18-Jan-2018.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
nnelOLD  |-  ( -.  A  e/  B  <->  A  e.  B )

Proof of Theorem nnelOLD
StepHypRef Expression
1 notnot 289 . . 3  |-  ( A  e.  B  <->  -.  -.  A  e.  B )
21bicomi 202 . 2  |-  ( -. 
-.  A  e.  B  <->  A  e.  B )
3 df-nel 2601 . 2  |-  ( A  e/  B  <->  -.  A  e.  B )
42, 3xchnxbir 307 1  |-  ( -.  A  e/  B  <->  A  e.  B )
Colors of variables: wff setvar class
Syntax hints:   -. wn 3    <-> wb 184    e. wcel 1842    e/ wnel 2599
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 185  df-nel 2601
This theorem is referenced by: (None)
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