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Theorem nnelOLD 2803
Description: Obsolete proof of nnel 2802 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

Proof of Theorem nnelOLD
StepHypRef Expression
1 notnot 291 . . 3
21bicomi 202 . 2
3 df-nel 2655 . 2
42, 3xchnxbir 309 1
Colors of variables: wff setvar class
Syntax hints:  -.wn 3  <->wb 184  e.wcel 1818  e/wnel 2653
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 2655
  Copyright terms: Public domain W3C validator