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Theorem notnotri 133
Description: Inference associated with notnotr 132. For a shorter proof using ax-2 7, see notnotriALT 134. (Contributed by NM, 27-Feb-2008.) (Proof shortened by Wolf Lammen, 15-Jul-2021.) Remove dependency on ax-2 7. (Revised by Steven Nguyen, 27-Dec-2022.)
Hypothesis
Ref Expression
notnotri.1 ¬ ¬ 𝜑
Assertion
Ref Expression
notnotri 𝜑

Proof of Theorem notnotri
StepHypRef Expression
1 notnotri.1 . 2 ¬ ¬ 𝜑
21pm2.21i 119 . 2 𝜑 → ¬ ¬ ¬ 𝜑)
31, 2mt4 116 1 𝜑
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-3 8
This theorem is referenced by:  mt3  204  pm2.65ni  41535
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