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Theorem anor 981
Description: Conjunction in terms of disjunction (De Morgan's law). Theorem *4.5 of [WhiteheadRussell] p. 120. (Contributed by NM, 3-Jan-1993.) (Proof shortened by Wolf Lammen, 3-Nov-2012.)
Assertion
Ref Expression
anor ((𝜑𝜓) ↔ ¬ (¬ 𝜑 ∨ ¬ 𝜓))

Proof of Theorem anor
StepHypRef Expression
1 notnotb 314 . 2 ((𝜑𝜓) ↔ ¬ ¬ (𝜑𝜓))
2 ianor 980 . 2 (¬ (𝜑𝜓) ↔ (¬ 𝜑 ∨ ¬ 𝜓))
31, 2xchbinx 333 1 ((𝜑𝜓) ↔ ¬ (¬ 𝜑 ∨ ¬ 𝜓))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 205  wa 396  wo 845
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 206  df-an 397  df-or 846
This theorem is referenced by:  pm3.1  990  pm3.11  991  dn1  1056  noran  1533  bropopvvv  8072  swrdnd0  14603  dflim5  42064  ifpananb  42242  iunrelexp0  42438
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