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Theorem notnotrALT 38256
Description: Converse of double negation. Alternate proof of notnotr 125. This proof is notnotrALTVD 38673 automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
notnotrALT (¬ ¬ 𝜑𝜑)

Proof of Theorem notnotrALT
StepHypRef Expression
1 id 22 . 2 (¬ ¬ 𝜑 → ¬ ¬ 𝜑)
2 pm2.21 120 . 2 (¬ ¬ 𝜑 → (¬ 𝜑 → ¬ ¬ ¬ 𝜑))
31, 2mt4d 152 1 (¬ ¬ 𝜑𝜑)
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem is referenced by: (None)
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