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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  2876  ifnot  3508  eupath2  23075  vk15.4j  26984  zfregs2VD  27307  vk15.4jVD  27380  con3ALTVD  27382
This theorem was proved from axioms:  ax-1 7  ax-2 8  ax-3 9  ax-mp 10
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