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Theorem nfanOLD 1826
 Description: Obsolete proof of nfan 1824 as of 2-Jan-2018. (Contributed by Mario Carneiro, 11-Aug-2016.) (New usage is discouraged.)
Hypotheses
Ref Expression
nfan.1 xφ
nfan.2 xψ
Assertion
Ref Expression
nfanOLD x(φ ψ)

Proof of Theorem nfanOLD
StepHypRef Expression
1 df-an 360 . 2 ((φ ψ) ↔ ¬ (φ → ¬ ψ))
2 nfan.1 . . . 4 xφ
3 nfan.2 . . . . 5 xψ
43nfn 1793 . . . 4 x ¬ ψ
52, 4nfim 1813 . . 3 x(φ → ¬ ψ)
65nfn 1793 . 2 x ¬ (φ → ¬ ψ)
71, 6nfxfr 1570 1 x(φ ψ)
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 358  Ⅎwnf 1544 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-11 1746 This theorem depends on definitions:  df-bi 177  df-an 360  df-tru 1319  df-ex 1542  df-nf 1545 This theorem is referenced by: (None)
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