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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 21 . 2  |-  ( -. 
ph  ->  -.  ph )
21con2i 114 1  |-  ( ph  ->  -.  -.  ph )
Colors of variables: wff set class
Syntax hints:   -. wn 5    -> wi 6
This theorem is referenced by:  notnoti  117  con1d  118  con4i  124  notnot  284  biortn  397  pm2.13  409  eueq2  2914  ifnot  3577  eupath2  23276  stoweidlem39  27123  atbiffatnnbalt  27172  vk15.4j  27344  zfregs2VD  27667  vk15.4jVD  27740  con3ALTVD  27742  ax9dgenK  28174
This theorem was proved from axioms:  ax-1 7  ax-2 8  ax-3 9  ax-mp 10
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