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Theorem notnotdOLD 303
Description: Obsolete proof of notnotd 136 as of 27-Mar-2021. (Contributed by Jarvin Udandy, 2-Sep-2016.) (New usage is discouraged.) (Proof modification is discouraged.)
Hypothesis
Ref Expression
notnotdOLD.1 (𝜑𝜓)
Assertion
Ref Expression
notnotdOLD (𝜑 → ¬ ¬ 𝜓)

Proof of Theorem notnotdOLD
StepHypRef Expression
1 notnotdOLD.1 . 2 (𝜑𝜓)
2 notnotb 302 . 2 (𝜓 ↔ ¬ ¬ 𝜓)
31, 2sylib 206 1 (𝜑 → ¬ ¬ 𝜓)
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 depends on definitions:  df-bi 195
This theorem is referenced by: (None)
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