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Theorem nfbiOLD 2279
 Description: Obsolete proof of nfbi 1873 as of 6-Oct-2021. (Contributed by NM, 26-May-1993.) (Revised by Mario Carneiro, 11-Aug-2016.) (Proof shortened by Wolf Lammen, 2-Jan-2018.) (New usage is discouraged.) (Proof modification is discouraged.)
Hypotheses
Ref Expression
nfOLD.1 𝑥𝜑
nfOLD.2 𝑥𝜓
Assertion
Ref Expression
nfbiOLD 𝑥(𝜑𝜓)

Proof of Theorem nfbiOLD
StepHypRef Expression
1 nfOLD.1 . . . 4 𝑥𝜑
21a1i 11 . . 3 (⊤ → Ⅎ𝑥𝜑)
3 nfOLD.2 . . . 4 𝑥𝜓
43a1i 11 . . 3 (⊤ → Ⅎ𝑥𝜓)
52, 4nfbidOLD 2278 . 2 (⊤ → Ⅎ𝑥(𝜑𝜓))
65trud 1533 1 𝑥(𝜑𝜓)
 Colors of variables: wff setvar class Syntax hints:   ↔ wb 196  ⊤wtru 1524  ℲwnfOLD 1749 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1762  ax-4 1777  ax-5 1879  ax-6 1945  ax-7 1981  ax-10 2059  ax-12 2087 This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-tru 1526  df-ex 1745  df-nf 1750  df-nfOLD 1761 This theorem is referenced by: (None)
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