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Theorem notnot1 114
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 19 . 2  |-  ( -. 
ph  ->  -.  ph )
21con2i 112 1  |-  ( ph  ->  -.  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4
This theorem is referenced by:  notnoti  115  con1d  116  con4i  122  notnot  282  biortn  395  pm2.13  407  eueq2  2939  ifnot  3603  eupath2  23904  stoweidlem39  27788  atbiffatnnbalt  27883  nbusgra  28143  vk15.4j  28291  zfregs2VD  28617  vk15.4jVD  28690  con3ALTVD  28692
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
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