Theorem dfss4 4209

Description: Subclass defined in terms of class difference. See comments under dfun2 4210. (Contributed by NM, 22-Mar-1998.) (Proof shortened by Andrew Salmon, 26-Jun-2011.)

Assertion

Ref	Expression
dfss4	⊢ (𝐴 ⊆ 𝐵 ↔ (𝐵 ∖ (𝐵 ∖ 𝐴)) = 𝐴)

Proof of Theorem dfss4

Dummy variable 𝑥 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		sseqin2 4166	. 2 ⊢ (𝐴 ⊆ 𝐵 ↔ (𝐵 ∩ 𝐴) = 𝐴)
2		eldif 3911	. . . . . . 7 ⊢ (𝑥 ∈ (𝐵 ∖ 𝐴) ↔ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴))
3	2	notbii 320	. . . . . 6 ⊢ (¬ 𝑥 ∈ (𝐵 ∖ 𝐴) ↔ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴))
4	3	anbi2i 624	. . . . 5 ⊢ ((𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ (𝐵 ∖ 𝐴)) ↔ (𝑥 ∈ 𝐵 ∧ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴)))
5		elin 3917	. . . . . 6 ⊢ (𝑥 ∈ (𝐵 ∩ 𝐴) ↔ (𝑥 ∈ 𝐵 ∧ 𝑥 ∈ 𝐴))
6		abai 825	. . . . . 6 ⊢ ((𝑥 ∈ 𝐵 ∧ 𝑥 ∈ 𝐴) ↔ (𝑥 ∈ 𝐵 ∧ (𝑥 ∈ 𝐵 → 𝑥 ∈ 𝐴)))
7		iman 403	. . . . . . 7 ⊢ ((𝑥 ∈ 𝐵 → 𝑥 ∈ 𝐴) ↔ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴))
8	7	anbi2i 624	. . . . . 6 ⊢ ((𝑥 ∈ 𝐵 ∧ (𝑥 ∈ 𝐵 → 𝑥 ∈ 𝐴)) ↔ (𝑥 ∈ 𝐵 ∧ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴)))
9	5, 6, 8	3bitri 297	. . . . 5 ⊢ (𝑥 ∈ (𝐵 ∩ 𝐴) ↔ (𝑥 ∈ 𝐵 ∧ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴)))
10	4, 9	bitr4i 278	. . . 4 ⊢ ((𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ (𝐵 ∖ 𝐴)) ↔ 𝑥 ∈ (𝐵 ∩ 𝐴))
11	10	difeqri 4075	. . 3 ⊢ (𝐵 ∖ (𝐵 ∖ 𝐴)) = (𝐵 ∩ 𝐴)
12	11	eqeq1i 2742	. 2 ⊢ ((𝐵 ∖ (𝐵 ∖ 𝐴)) = 𝐴 ↔ (𝐵 ∩ 𝐴) = 𝐴)
13	1, 12	bitr4i 278	1 ⊢ (𝐴 ⊆ 𝐵 ↔ (𝐵 ∖ (𝐵 ∖ 𝐴)) = 𝐴)

Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 205   ∧ wa 397   = wceq 1541   ∈ wcel 2106   ∖ cdif 3898   ∩ cin 3900   ⊆ wss 3901

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1913  ax-6 1971  ax-7 2011  ax-8 2108  ax-9 2116  ax-ext 2708

This theorem depends on definitions:  df-bi 206  df-an 398  df-tru 1544  df-ex 1782  df-sb 2068  df-clab 2715  df-cleq 2729  df-clel 2815  df-rab 3405  df-v 3444  df-dif 3904  df-in 3908  df-ss 3918

This theorem is referenced by:  ssdifim  4213  dfin4  4218  sscon34b  4245  sorpsscmpl  7653  sbthlem3  8954  fin23lem7  10177  fin23lem11  10178  compsscnvlem  10231  compssiso  10235  isf34lem4  10238  efgmnvl  19415  frlmlbs  21109  isopn2  22288  iincld  22295  iuncld  22301  clsval2  22306  ntrval2  22307  ntrdif  22308  clsdif  22309  cmclsopn  22318  opncldf1  22340  indiscld  22347  mretopd  22348  restcld  22428  pnrmopn  22599  conndisj  22672  hausllycmp  22750  kqcldsat  22989  filufint  23176  cfinufil  23184  ufilen  23186  alexsublem  23300  bcth3  24600  inmbl  24811  iccmbl  24835  mbfimaicc  24900  i1fd  24950  itgss3  25084  difuncomp  31178  iundifdifd  31186  iundifdif  31187  supppreima  31310  pmtrcnelor  31645  ist0cld  32079  cldssbrsiga  32451  unelcarsg  32577  kur14lem4  33468  cldbnd  34652  clsun  34654  mblfinlem3  35972  mblfinlem4  35973  ismblfin  35974  itg2addnclem  35984  fdc  36059  dssmapnvod  42001  ntrclsfveq1  42043  ntrclsfveq  42045  ntrclsneine0lem  42047  ntrclsiso  42050  ntrclsk2  42051  ntrclskb  42052  ntrclsk3  42053  ntrclsk13  42054  ntrclsk4  42055  clsneiel2  42092  neicvgel2  42103  salincl  44252  salexct  44261  ovnsubadd2lem  44572  lincext2  46214  opncldeqv  46613