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Theorem notnotri 108
Description: Inference from double negation. (Contributed by NM, 27-Feb-2008.)
Hypothesis
Ref Expression
notnotri.1  |-  -.  -.  ph
Assertion
Ref Expression
notnotri  |-  ph

Proof of Theorem notnotri
StepHypRef Expression
1 notnotri.1 . 2  |-  -.  -.  ph
2 notnot2 106 . 2  |-  ( -. 
-.  ph  ->  ph )
31, 2ax-mp 8 1  |-  ph
Colors of variables: wff set class
Syntax hints:   -. wn 3
This theorem is referenced by:  mt3  173  mtp-xor  1545
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
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