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Theorem pm5.19 374
Description: Theorem *5.19 of [WhiteheadRussell] p. 124. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm5.19 ¬ (𝜑 ↔ ¬ 𝜑)

Proof of Theorem pm5.19
StepHypRef Expression
1 biid 250 . 2 (𝜑𝜑)
2 pm5.18 370 . 2 ((𝜑𝜑) ↔ ¬ (𝜑 ↔ ¬ 𝜑))
31, 2mpbi 219 1 ¬ (𝜑 ↔ ¬ 𝜑)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wb 195
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 196
This theorem is referenced by:  xorexmid  1472  ru  3401  pwfseqlem1  9359  bisym1  31588  bj-ru0  32124  rusbcALT  37662
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