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Theorem pm4.8 378
Description: Theorem *4.8 of [WhiteheadRussell] p. 122. (Contributed by NM, 3-Jan-2005.)
Assertion
Ref Expression
pm4.8 ((𝜑 → ¬ 𝜑) ↔ ¬ 𝜑)

Proof of Theorem pm4.8
StepHypRef Expression
1 pm2.01 178 . 2 ((𝜑 → ¬ 𝜑) → ¬ 𝜑)
2 ax-1 6 . 2 𝜑 → (𝜑 → ¬ 𝜑))
31, 2impbii 197 1 ((𝜑 → ¬ 𝜑) ↔ ¬ 𝜑)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 194
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 195
This theorem is referenced by:  wl-nannot  32281  ifpimimb  36671
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