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Theorem nnnotnotr 15013
Description: Double negation of double negation elimination. Suggested by an online post by Martin Escardo. Although this statement resembles nnexmid 851, it can be proved with reference only to implication and negation (that is, without use of disjunction). (Contributed by Jim Kingdon, 21-Oct-2024.)
Assertion
Ref Expression
nnnotnotr  |-  -.  -.  ( -.  -.  ph  ->  ph )

Proof of Theorem nnnotnotr
StepHypRef Expression
1 conax1 654 . 2  |-  ( -.  ( -.  -.  ph  ->  ph )  ->  -.  ph )
2 pm2.24 622 . . 3  |-  ( -. 
ph  ->  ( -.  -.  ph 
->  ph ) )
32con3i 633 . 2  |-  ( -.  ( -.  -.  ph  ->  ph )  ->  -.  -.  ph )
41, 3pm2.65i 640 1  |-  -.  -.  ( -.  -.  ph  ->  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-in1 615  ax-in2 616
This theorem is referenced by: (None)
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