Theorem ssddif 3198

Description: Double complement and subset. Similar to ddifss 3202 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 ⊆ 𝐵 ↔ (𝐵 ∖ (𝐵 ∖ 𝐴)) = 𝐴). (Contributed by Jim Kingdon, 24-Jul-2018.)

Assertion

Ref	Expression
ssddif	⊢ (𝐴 ⊆ 𝐵 ↔ 𝐴 ⊆ (𝐵 ∖ (𝐵 ∖ 𝐴)))

Proof of Theorem ssddif

Dummy variable 𝑥 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		ancr 314	. . . . 5 ⊢ ((𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵) → (𝑥 ∈ 𝐴 → (𝑥 ∈ 𝐵 ∧ 𝑥 ∈ 𝐴)))
2		simpr 108	. . . . . . . 8 ⊢ ((𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴) → ¬ 𝑥 ∈ 𝐴)
3	2	con2i 589	. . . . . . 7 ⊢ (𝑥 ∈ 𝐴 → ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴))
4	3	anim2i 334	. . . . . 6 ⊢ ((𝑥 ∈ 𝐵 ∧ 𝑥 ∈ 𝐴) → (𝑥 ∈ 𝐵 ∧ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴)))
5		eldif 2982	. . . . . . 7 ⊢ (𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴)) ↔ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ (𝐵 ∖ 𝐴)))
6		eldif 2982	. . . . . . . . 9 ⊢ (𝑥 ∈ (𝐵 ∖ 𝐴) ↔ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴))
7	6	notbii 626	. . . . . . . 8 ⊢ (¬ 𝑥 ∈ (𝐵 ∖ 𝐴) ↔ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴))
8	7	anbi2i 444	. . . . . . 7 ⊢ ((𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ (𝐵 ∖ 𝐴)) ↔ (𝑥 ∈ 𝐵 ∧ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴)))
9	5, 8	bitri 182	. . . . . 6 ⊢ (𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴)) ↔ (𝑥 ∈ 𝐵 ∧ ¬ (𝑥 ∈ 𝐵 ∧ ¬ 𝑥 ∈ 𝐴)))
10	4, 9	sylibr 132	. . . . 5 ⊢ ((𝑥 ∈ 𝐵 ∧ 𝑥 ∈ 𝐴) → 𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴)))
11	1, 10	syl6 33	. . . 4 ⊢ ((𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵) → (𝑥 ∈ 𝐴 → 𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴))))
12		eldifi 3094	. . . . 5 ⊢ (𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴)) → 𝑥 ∈ 𝐵)
13	12	imim2i 12	. . . 4 ⊢ ((𝑥 ∈ 𝐴 → 𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴))) → (𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵))
14	11, 13	impbii 124	. . 3 ⊢ ((𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵) ↔ (𝑥 ∈ 𝐴 → 𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴))))
15	14	albii 1399	. 2 ⊢ (∀𝑥(𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵) ↔ ∀𝑥(𝑥 ∈ 𝐴 → 𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴))))
16		dfss2 2988	. 2 ⊢ (𝐴 ⊆ 𝐵 ↔ ∀𝑥(𝑥 ∈ 𝐴 → 𝑥 ∈ 𝐵))
17		dfss2 2988	. 2 ⊢ (𝐴 ⊆ (𝐵 ∖ (𝐵 ∖ 𝐴)) ↔ ∀𝑥(𝑥 ∈ 𝐴 → 𝑥 ∈ (𝐵 ∖ (𝐵 ∖ 𝐴))))
18	15, 16, 17	3bitr4i 210	1 ⊢ (𝐴 ⊆ 𝐵 ↔ 𝐴 ⊆ (𝐵 ∖ (𝐵 ∖ 𝐴)))

Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 102   ↔ wb 103  ∀wal 1282   ∈ wcel 1433   ∖ cdif 2970   ⊆ wss 2973

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 576  ax-in2 577  ax-io 662  ax-5 1376  ax-7 1377  ax-gen 1378  ax-ie1 1422  ax-ie2 1423  ax-8 1435  ax-10 1436  ax-11 1437  ax-i12 1438  ax-bndl 1439  ax-4 1440  ax-17 1459  ax-i9 1463  ax-ial 1467  ax-i5r 1468  ax-ext 2063

This theorem depends on definitions:  df-bi 115  df-tru 1287  df-nf 1390  df-sb 1686  df-clab 2068  df-cleq 2074  df-clel 2077  df-nfc 2208  df-v 2603  df-dif 2975  df-in 2979  df-ss 2986

This theorem is referenced by:  ddifss  3202  inssddif  3205