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Theorem notnot2ALT 28292
Description: Converse of double negation. Alternate proof of notnot2 104. This proof is notnot2ALTVD 28691 automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
notnot2ALT  |-  ( -. 
-.  ph  ->  ph )

Proof of Theorem notnot2ALT
StepHypRef Expression
1 id 19 . 2  |-  ( -. 
-.  ph  ->  -.  -.  ph )
2 pm2.21 100 . 2  |-  ( -. 
-.  ph  ->  ( -. 
ph  ->  -.  -.  -.  ph ) )
31, 2mt4d 130 1  |-  ( -. 
-.  ph  ->  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
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