Theorem ddifss 3359

Description: Double complement under universal class. In classical logic (or given an additional hypothesis, as in ddifnel 3252), 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

Step	Hyp	Ref	Expression
1		ssv 3163	. 2 |- A C_ _V
2		ssddif 3355	. 2 |- ( A C_ _V <-> A C_ ( _V \ ( _V \ A ) ) )
3	1, 2	mpbi 144	1 |- A C_ ( _V \ ( _V \ A ) )

Syntax hints:   _Vcvv 2725   \ cdif 3112   C_ wss 3115

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605  ax-io 699  ax-5 1435  ax-7 1436  ax-gen 1437  ax-ie1 1481  ax-ie2 1482  ax-8 1492  ax-10 1493  ax-11 1494  ax-i12 1495  ax-bndl 1497  ax-4 1498  ax-17 1514  ax-i9 1518  ax-ial 1522  ax-i5r 1523  ax-ext 2147

This theorem depends on definitions:  df-bi 116  df-tru 1346  df-nf 1449  df-sb 1751  df-clab 2152  df-cleq 2158  df-clel 2161  df-nfc 2296  df-v 2727  df-dif 3117  df-in 3121  df-ss 3128

This theorem is referenced by:  ssindif0im  3467  difdifdirss  3492