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Theorem notnot1 116
Description: Converse of double negation. Theorem *2.12 of [WhiteheadRussell] p. 101. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 2-Mar-2013.)
Assertion
Ref Expression
notnot1  |-  ( ph  ->  -.  -.  ph )

Proof of Theorem notnot1
StepHypRef Expression
1 id 20 . 2  |-  ( -. 
ph  ->  -.  ph )
21con2i 114 1  |-  ( ph  ->  -.  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4
This theorem is referenced by:  notnoti  117  con1d  118  con4i  124  notnot  283  biortn  396  pm2.13  408  eueq2  3068  ifnot  3737  nbusgra  21393  wlkntrl  21515  eupath2  21655  stoweidlem39  27655  vk15.4j  28323  zfregs2VD  28662  vk15.4jVD  28735  con3ALTVD  28737
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
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