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Axiom ax-frege41 36955
Description: The affirmation of 𝜑 denies the denial of 𝜑. Identical to notnot 134. Axiom 41 of [Frege1879] p. 47. (Contributed by RP, 24-Dec-2019.) (New usage is discouraged.)
Assertion
Ref Expression
ax-frege41 (𝜑 → ¬ ¬ 𝜑)

Detailed syntax breakdown of Axiom ax-frege41
StepHypRef Expression
1 wph . 2 wff 𝜑
21wn 3 . . 3 wff ¬ 𝜑
32wn 3 . 2 wff ¬ ¬ 𝜑
41, 3wi 4 1 wff (𝜑 → ¬ ¬ 𝜑)
Colors of variables: wff setvar class
This axiom is referenced by:  frege42  36956
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