Theorem ssunsn2 4782

Description: The property of being sandwiched between two sets naturally splits under union with a singleton. This is the induction hypothesis for the determination of large powersets such as pwtp 4828. (Contributed by Mario Carneiro, 2-Jul-2016.)

Assertion

Ref	Expression
ssunsn2	⊢ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ∨ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷}))))

Proof of Theorem ssunsn2

Step	Hyp	Ref	Expression
1		snssi 4742	. . . . 5 ⊢ (𝐷 ∈ 𝐴 → {𝐷} ⊆ 𝐴)
2		unss 4188	. . . . . . 7 ⊢ ((𝐵 ⊆ 𝐴 ∧ {𝐷} ⊆ 𝐴) ↔ (𝐵 ∪ {𝐷}) ⊆ 𝐴)
3	2	bicomi 227	. . . . . 6 ⊢ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ↔ (𝐵 ⊆ 𝐴 ∧ {𝐷} ⊆ 𝐴))
4	3	rbaibr 547	. . . . 5 ⊢ ({𝐷} ⊆ 𝐴 → (𝐵 ⊆ 𝐴 ↔ (𝐵 ∪ {𝐷}) ⊆ 𝐴))
5	1, 4	syl 18	. . . 4 ⊢ (𝐷 ∈ 𝐴 → (𝐵 ⊆ 𝐴 ↔ (𝐵 ∪ {𝐷}) ⊆ 𝐴))
6	5	anbi1d 643	. . 3 ⊢ (𝐷 ∈ 𝐴 → ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ↔ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷}))))
7	2	biimpi 219	. . . . . . 7 ⊢ ((𝐵 ⊆ 𝐴 ∧ {𝐷} ⊆ 𝐴) → (𝐵 ∪ {𝐷}) ⊆ 𝐴)
8	7	expcom 419	. . . . . 6 ⊢ ({𝐷} ⊆ 𝐴 → (𝐵 ⊆ 𝐴 → (𝐵 ∪ {𝐷}) ⊆ 𝐴))
9	1, 8	syl 18	. . . . 5 ⊢ (𝐷 ∈ 𝐴 → (𝐵 ⊆ 𝐴 → (𝐵 ∪ {𝐷}) ⊆ 𝐴))
10		ssun3 4178	. . . . . 6 ⊢ (𝐴 ⊆ 𝐶 → 𝐴 ⊆ (𝐶 ∪ {𝐷}))
11	10	a1i 11	. . . . 5 ⊢ (𝐷 ∈ 𝐴 → (𝐴 ⊆ 𝐶 → 𝐴 ⊆ (𝐶 ∪ {𝐷})))
12	9, 11	anim12d 621	. . . 4 ⊢ (𝐷 ∈ 𝐴 → ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) → ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷}))))
13		pm4.72 964	. . . 4 ⊢ (((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) → ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷}))) ↔ (((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ∨ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})))))
14	12, 13	sylib 221	. . 3 ⊢ (𝐷 ∈ 𝐴 → (((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ∨ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})))))
15	6, 14	bitrd 282	. 2 ⊢ (𝐷 ∈ 𝐴 → ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ∨ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})))))
16		uncom 4157	. . . . . . 7 ⊢ ({𝐷} ∪ 𝐶) = (𝐶 ∪ {𝐷})
17	16	sseq2i 3937	. . . . . 6 ⊢ (𝐴 ⊆ ({𝐷} ∪ 𝐶) ↔ 𝐴 ⊆ (𝐶 ∪ {𝐷}))
18		ssundif 4442	. . . . . 6 ⊢ (𝐴 ⊆ ({𝐷} ∪ 𝐶) ↔ (𝐴 ∖ {𝐷}) ⊆ 𝐶)
19	17, 18	bitr3i 280	. . . . 5 ⊢ (𝐴 ⊆ (𝐶 ∪ {𝐷}) ↔ (𝐴 ∖ {𝐷}) ⊆ 𝐶)
20		disjsn 4668	. . . . . . 7 ⊢ ((𝐴 ∩ {𝐷}) = ∅ ↔ ¬ 𝐷 ∈ 𝐴)
21		disj3 4406	. . . . . . 7 ⊢ ((𝐴 ∩ {𝐷}) = ∅ ↔ 𝐴 = (𝐴 ∖ {𝐷}))
22	20, 21	bitr3i 280	. . . . . 6 ⊢ (¬ 𝐷 ∈ 𝐴 ↔ 𝐴 = (𝐴 ∖ {𝐷}))
23		sseq1 3933	. . . . . 6 ⊢ (𝐴 = (𝐴 ∖ {𝐷}) → (𝐴 ⊆ 𝐶 ↔ (𝐴 ∖ {𝐷}) ⊆ 𝐶))
24	22, 23	sylbi 220	. . . . 5 ⊢ (¬ 𝐷 ∈ 𝐴 → (𝐴 ⊆ 𝐶 ↔ (𝐴 ∖ {𝐷}) ⊆ 𝐶))
25	19, 24	bitr4id 293	. . . 4 ⊢ (¬ 𝐷 ∈ 𝐴 → (𝐴 ⊆ (𝐶 ∪ {𝐷}) ↔ 𝐴 ⊆ 𝐶))
26	25	anbi2d 642	. . 3 ⊢ (¬ 𝐷 ∈ 𝐴 → ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ↔ (𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶)))
27	3	simplbi 502	. . . . . . 7 ⊢ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 → 𝐵 ⊆ 𝐴)
28	27	a1i 11	. . . . . 6 ⊢ (¬ 𝐷 ∈ 𝐴 → ((𝐵 ∪ {𝐷}) ⊆ 𝐴 → 𝐵 ⊆ 𝐴))
29	25	biimpd 232	. . . . . 6 ⊢ (¬ 𝐷 ∈ 𝐴 → (𝐴 ⊆ (𝐶 ∪ {𝐷}) → 𝐴 ⊆ 𝐶))
30	28, 29	anim12d 621	. . . . 5 ⊢ (¬ 𝐷 ∈ 𝐴 → (((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) → (𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶)))
31		pm4.72 964	. . . . 5 ⊢ ((((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) → (𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶)) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ↔ (((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ∨ (𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶))))
32	30, 31	sylib 221	. . . 4 ⊢ (¬ 𝐷 ∈ 𝐴 → ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ↔ (((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ∨ (𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶))))
33		orcom 884	. . . 4 ⊢ ((((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ∨ (𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶)) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ∨ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷}))))
34	32, 33	bitrdi 290	. . 3 ⊢ (¬ 𝐷 ∈ 𝐴 → ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ∨ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})))))
35	26, 34	bitrd 282	. 2 ⊢ (¬ 𝐷 ∈ 𝐴 → ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ∨ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})))))
36	15, 35	pm2.61i 184	1 ⊢ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷})) ↔ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ⊆ 𝐶) ∨ ((𝐵 ∪ {𝐷}) ⊆ 𝐴 ∧ 𝐴 ⊆ (𝐶 ∪ {𝐷}))))

This proof depends on syntax axioms:  ¬ wn 3   → wi 4   ↔ wb 209   ∧ wa 401   ∨ wo 861   = wceq 1569   ∈ wcel 2144   ⊆ wss 3895   ∖ cdif 4045   ∩ cin 4089   ∪ cun 4149  ∅c0 4278  {csn 4584

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1827  ax-4 1841  ax-5 1942  ax-6 1999  ax-7 2040  ax-8 2146  ax-9 2154  ax-ext 2732

This proof depends on definitions:  df-bi 210  df-an 402  df-or 862  df-tru 1572  df-fal 1582  df-ex 1812  df-sb 2099  df-clab 2739  df-cleq 2752  df-clel 2835  df-ral 3077  df-v 3452  df-ss 3896  df-dif 4047  df-in 4091  df-un 4151  df-nul 4279  df-sn 4585

This theorem is used by:  ssunsn  4783  ssunpr  4788  sstp  4790