Theorem ssddif 3356

Description: Double complement and subset. Similar to ddifss 3360 but inside a class B instead of the universal class _V. In classical logic the subset operation on the right hand side could be an equality (that is, A C_ B <-> ( B \ ( B \ A ) ) = A). (Contributed by Jim Kingdon, 24-Jul-2018.)

Assertion

Ref	Expression
ssddif	|- ( A C_ B <-> A C_ ( B \ ( B \ A ) ) )

Proof of Theorem ssddif

Dummy variable x is distinct from all other variables.

Step	Hyp	Ref	Expression
1		ancr 319	. . . . 5 |- ( ( x e. A -> x e. B ) -> ( x e. A -> ( x e. B /\ x e. A ) ) )
2		simpr 109	. . . . . . . 8 |- ( ( x e. B /\ -. x e. A ) -> -. x e. A )
3	2	con2i 617	. . . . . . 7 |- ( x e. A -> -. ( x e. B /\ -. x e. A ) )
4	3	anim2i 340	. . . . . 6 |- ( ( x e. B /\ x e. A ) -> ( x e. B /\ -. ( x e. B /\ -. x e. A ) ) )
5		eldif 3125	. . . . . . 7 |- ( x e. ( B \ ( B \ A ) ) <-> ( x e. B /\ -. x e. ( B \ A ) ) )
6		eldif 3125	. . . . . . . . 9 |- ( x e. ( B \ A ) <-> ( x e. B /\ -. x e. A ) )
7	6	notbii 658	. . . . . . . 8 |- ( -. x e. ( B \ A ) <-> -. ( x e. B /\ -. x e. A ) )
8	7	anbi2i 453	. . . . . . 7 |- ( ( x e. B /\ -. x e. ( B \ A ) ) <-> ( x e. B /\ -. ( x e. B /\ -. x e. A ) ) )
9	5, 8	bitri 183	. . . . . 6 |- ( x e. ( B \ ( B \ A ) ) <-> ( x e. B /\ -. ( x e. B /\ -. x e. A ) ) )
10	4, 9	sylibr 133	. . . . 5 |- ( ( x e. B /\ x e. A ) -> x e. ( B \ ( B \ A ) ) )
11	1, 10	syl6 33	. . . 4 |- ( ( x e. A -> x e. B ) -> ( x e. A -> x e. ( B \ ( B \ A ) ) ) )
12		eldifi 3244	. . . . 5 |- ( x e. ( B \ ( B \ A ) ) -> x e. B )
13	12	imim2i 12	. . . 4 |- ( ( x e. A -> x e. ( B \ ( B \ A ) ) ) -> ( x e. A -> x e. B ) )
14	11, 13	impbii 125	. . 3 |- ( ( x e. A -> x e. B ) <-> ( x e. A -> x e. ( B \ ( B \ A ) ) ) )
15	14	albii 1458	. 2 |- ( A. x ( x e. A -> x e. B ) <-> A. x ( x e. A -> x e. ( B \ ( B \ A ) ) ) )
16		dfss2 3131	. 2 |- ( A C_ B <-> A. x ( x e. A -> x e. B ) )
17		dfss2 3131	. 2 |- ( A C_ ( B \ ( B \ A ) ) <-> A. x ( x e. A -> x e. ( B \ ( B \ A ) ) ) )
18	15, 16, 17	3bitr4i 211	1 |- ( A C_ B <-> A C_ ( B \ ( B \ A ) ) )

Syntax hints:   -. wn 3   -> wi 4   /\ wa 103   <-> wb 104   A.wal 1341   e. wcel 2136   \ cdif 3113   C_ wss 3116

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 2297  df-v 2728  df-dif 3118  df-in 3122  df-ss 3129

This theorem is referenced by:  ddifss  3360  inssddif  3363