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Theorem ddifss 3203
Description: Double complement under universal class. In classical logic (or given an additional hypothesis, as in ddifnel 3104), this is equality rather than subset. (Contributed by Jim Kingdon, 24-Jul-2018.)
Assertion
Ref Expression
ddifss  |-  A  C_  ( _V  \  ( _V  \  A ) )

Proof of Theorem ddifss
StepHypRef Expression
1 ssv 3020 . 2  |-  A  C_  _V
2 ssddif 3199 . 2  |-  ( A 
C_  _V  <->  A  C_  ( _V 
\  ( _V  \  A ) ) )
31, 2mpbi 143 1  |-  A  C_  ( _V  \  ( _V  \  A ) )
Colors of variables: wff set class
Syntax hints:   _Vcvv 2602    \ cdif 2971    C_ wss 2974
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-in1 577  ax-in2 578  ax-io 663  ax-5 1377  ax-7 1378  ax-gen 1379  ax-ie1 1423  ax-ie2 1424  ax-8 1436  ax-10 1437  ax-11 1438  ax-i12 1439  ax-bndl 1440  ax-4 1441  ax-17 1460  ax-i9 1464  ax-ial 1468  ax-i5r 1469  ax-ext 2064
This theorem depends on definitions:  df-bi 115  df-tru 1288  df-nf 1391  df-sb 1687  df-clab 2069  df-cleq 2075  df-clel 2078  df-nfc 2209  df-v 2604  df-dif 2976  df-in 2980  df-ss 2987
This theorem is referenced by:  ssindif0im  3304  difdifdirss  3328
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