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Theorem nfexOLD 1844
 Description: Obsolete proof of nfex 1843 as of 30-Dec-2017. (Contributed by Mario Carneiro, 11-Aug-2016.) (Proof modification is discouraged.) (New usage is discouraged.)
Hypothesis
Ref Expression
nfal.1 xφ
Assertion
Ref Expression
nfexOLD xyφ

Proof of Theorem nfexOLD
StepHypRef Expression
1 df-ex 1542 . 2 (yφ ↔ ¬ y ¬ φ)
2 nfal.1 . . . . 5 xφ
32nfn 1793 . . . 4 x ¬ φ
43nfal 1842 . . 3 xy ¬ φ
54nfn 1793 . 2 x ¬ y ¬ φ
61, 5nfxfr 1570 1 xyφ
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3  ∀wal 1540  ∃wex 1541  Ⅎwnf 1544 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746 This theorem depends on definitions:  df-bi 177  df-tru 1319  df-ex 1542  df-nf 1545 This theorem is referenced by: (None)
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