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Theorem notnoti 117
Description: Infer double negation. (Contributed by NM, 27-Feb-2008.)
Hypothesis
Ref Expression
negbi.1  |-  ph
Assertion
Ref Expression
notnoti  |-  -.  -.  ph

Proof of Theorem notnoti
StepHypRef Expression
1 negbi.1 . 2  |-  ph
2 notnot1 116 . 2  |-  ( ph  ->  -.  -.  ph )
31, 2ax-mp 8 1  |-  -.  -.  ph
Colors of variables: wff set class
Syntax hints:   -. wn 3
This theorem is referenced by:  nbn3  338  fal  1331  19.2OLD  1713  ax9dgen  1731  mdegleb  19987  nextnt  26155  amosym1  26176  aisbnaxb  27855
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
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