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Theorem ax-9 1421
Description: Derive ax-9 1421 from ax-i9 1420, the modified version for intuitionistic logic. Although ax-9 1421 does hold intuistionistically, in intuitionistic logic it is weaker than ax-i9 1420. (Contributed by NM, 3-Feb-2015.)
Assertion
Ref Expression
ax-9

Proof of Theorem ax-9
StepHypRef Expression
1 ax-i9 1420 . . 3
21notnoti 573 . 2
3 alnex 1385 . 2
42, 3mtbir 595 1
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-ie2 1380  ax-i9 1420
This theorem depends on definitions:  df-bi 110  df-tru 1245  df-fal 1248
This theorem is referenced by:  equidqe  1422
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