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Theorem ax9vsep 3871
 Description: Derive a weakened version of ax-9 1421, where x and y must be distinct, from Separation ax-sep 3866 and Extensionality ax-ext 2019. In intuitionistic logic a9evsep 3870 is stronger and also holds. (Contributed by NM, 12-Nov-2013.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
ax9vsep ¬ x ¬ x = y
Distinct variable group:   x,y

Proof of Theorem ax9vsep
StepHypRef Expression
1 a9evsep 3870 . 2 x x = y
2 exalim 1388 . 2 (x x = y → ¬ x ¬ x = y)
31, 2ax-mp 7 1 ¬ x ¬ x = y
 Colors of variables: wff set class Syntax hints:  ¬ wn 3  ∀wal 1240   = wceq 1242  ∃wex 1378 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545  ax-5 1333  ax-gen 1335  ax-ie1 1379  ax-ie2 1380  ax-4 1397  ax-ial 1424  ax-ext 2019  ax-sep 3866 This theorem depends on definitions:  df-bi 110  df-tru 1245  df-fal 1248 This theorem is referenced by: (None)
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