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Theorem anor 984
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 315 . 2 ((𝜑𝜓) ↔ ¬ ¬ (𝜑𝜓))
2 ianor 983 . 2 (¬ (𝜑𝜓) ↔ (¬ 𝜑 ∨ ¬ 𝜓))
31, 2xchbinx 334 1 ((𝜑𝜓) ↔ ¬ (¬ 𝜑 ∨ ¬ 𝜓))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 206  wa 395  wo 847
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 207  df-an 396  df-or 848
This theorem is referenced by:  pm3.1  993  pm3.11  994  dn1  1057  noran  1529  bropopvvv  8114  swrdnd0  14692  dflim5  43319  ifpananb  43496  iunrelexp0  43692
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