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Theorem notnoti 123
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 122 . 2  |-  ( ph  ->  -.  -.  ph )
31, 2ax-mp 5 1  |-  -.  -.  ph
Colors of variables: wff setvar class
Syntax hints:   -. wn 3
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem is referenced by:  nbn3  348  fal  1377  ax6dgen  1764  mdegleb  21653  nextnt  28387  amosym1  28408  aisbnaxb  30065
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