Theorem ssfin4 10316

Description: Dedekind finite sets have Dedekind finite subsets. (Contributed by Stefan O'Rear, 30-Oct-2014.) (Revised by Mario Carneiro, 6-May-2015.) (Revised by Mario Carneiro, 16-May-2015.)

Assertion

Ref	Expression
ssfin4	⊢ ((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) → 𝐵 ∈ FinIV)

Proof of Theorem ssfin4

Dummy variables 𝑐 𝑥 are mutually distinct and distinct from all other variables.

Step	Hyp	Ref	Expression
1		simpll 779	. . . 4 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → 𝐴 ∈ FinIV)
2		pssss 4049	. . . . . . . . 9 ⊢ (𝑥 ⊊ 𝐵 → 𝑥 ⊆ 𝐵)
3		simpr 490	. . . . . . . . 9 ⊢ ((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) → 𝐵 ⊆ 𝐴)
4	2, 3	sylan9ssr 3948	. . . . . . . 8 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) → 𝑥 ⊆ 𝐴)
5		difssd 4087	. . . . . . . 8 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) → (𝐴 ∖ 𝐵) ⊆ 𝐴)
6	4, 5	unssd 4141	. . . . . . 7 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) → (𝑥 ∪ (𝐴 ∖ 𝐵)) ⊆ 𝐴)
7		pssnel 4427	. . . . . . . . 9 ⊢ (𝑥 ⊊ 𝐵 → ∃𝑐(𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥))
8	7	adantl 487	. . . . . . . 8 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) → ∃𝑐(𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥))
9		simpllr 788	. . . . . . . . . . 11 ⊢ ((((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) ∧ (𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥)) → 𝐵 ⊆ 𝐴)
10		simprl 783	. . . . . . . . . . 11 ⊢ ((((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) ∧ (𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥)) → 𝑐 ∈ 𝐵)
11	9, 10	sseldd 3935	. . . . . . . . . 10 ⊢ ((((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) ∧ (𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥)) → 𝑐 ∈ 𝐴)
12		simprr 785	. . . . . . . . . . 11 ⊢ ((((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) ∧ (𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥)) → ¬ 𝑐 ∈ 𝑥)
13		elndif 4083	. . . . . . . . . . . 12 ⊢ (𝑐 ∈ 𝐵 → ¬ 𝑐 ∈ (𝐴 ∖ 𝐵))
14	13	ad2antrl 741	. . . . . . . . . . 11 ⊢ ((((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) ∧ (𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥)) → ¬ 𝑐 ∈ (𝐴 ∖ 𝐵))
15		ioran 999	. . . . . . . . . . . 12 ⊢ (¬ (𝑐 ∈ 𝑥 ∨ 𝑐 ∈ (𝐴 ∖ 𝐵)) ↔ (¬ 𝑐 ∈ 𝑥 ∧ ¬ 𝑐 ∈ (𝐴 ∖ 𝐵)))
16		elun 4103	. . . . . . . . . . . 12 ⊢ (𝑐 ∈ (𝑥 ∪ (𝐴 ∖ 𝐵)) ↔ (𝑐 ∈ 𝑥 ∨ 𝑐 ∈ (𝐴 ∖ 𝐵)))
17	15, 16	xchnxbir 336	. . . . . . . . . . 11 ⊢ (¬ 𝑐 ∈ (𝑥 ∪ (𝐴 ∖ 𝐵)) ↔ (¬ 𝑐 ∈ 𝑥 ∧ ¬ 𝑐 ∈ (𝐴 ∖ 𝐵)))
18	12, 14, 17	sylanbrc 595	. . . . . . . . . 10 ⊢ ((((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) ∧ (𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥)) → ¬ 𝑐 ∈ (𝑥 ∪ (𝐴 ∖ 𝐵)))
19		nelneq2 2887	. . . . . . . . . 10 ⊢ ((𝑐 ∈ 𝐴 ∧ ¬ 𝑐 ∈ (𝑥 ∪ (𝐴 ∖ 𝐵))) → ¬ 𝐴 = (𝑥 ∪ (𝐴 ∖ 𝐵)))
20	11, 18, 19	syl2anc 596	. . . . . . . . 9 ⊢ ((((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) ∧ (𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥)) → ¬ 𝐴 = (𝑥 ∪ (𝐴 ∖ 𝐵)))
21		eqcom 2769	. . . . . . . . 9 ⊢ (𝐴 = (𝑥 ∪ (𝐴 ∖ 𝐵)) ↔ (𝑥 ∪ (𝐴 ∖ 𝐵)) = 𝐴)
22	20, 21	sylnib 331	. . . . . . . 8 ⊢ ((((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) ∧ (𝑐 ∈ 𝐵 ∧ ¬ 𝑐 ∈ 𝑥)) → ¬ (𝑥 ∪ (𝐴 ∖ 𝐵)) = 𝐴)
23	8, 22	exlimddv 1968	. . . . . . 7 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) → ¬ (𝑥 ∪ (𝐴 ∖ 𝐵)) = 𝐴)
24		dfpss2 4039	. . . . . . 7 ⊢ ((𝑥 ∪ (𝐴 ∖ 𝐵)) ⊊ 𝐴 ↔ ((𝑥 ∪ (𝐴 ∖ 𝐵)) ⊆ 𝐴 ∧ ¬ (𝑥 ∪ (𝐴 ∖ 𝐵)) = 𝐴))
25	6, 23, 24	sylanbrc 595	. . . . . 6 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ 𝑥 ⊊ 𝐵) → (𝑥 ∪ (𝐴 ∖ 𝐵)) ⊊ 𝐴)
26	25	adantrr 730	. . . . 5 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → (𝑥 ∪ (𝐴 ∖ 𝐵)) ⊊ 𝐴)
27		simprr 785	. . . . . . 7 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → 𝑥 ≈ 𝐵)
28		difexg 5298	. . . . . . . 8 ⊢ (𝐴 ∈ FinIV → (𝐴 ∖ 𝐵) ∈ V)
29		enrefg 8994	. . . . . . . 8 ⊢ ((𝐴 ∖ 𝐵) ∈ V → (𝐴 ∖ 𝐵) ≈ (𝐴 ∖ 𝐵))
30	1, 28, 29	3syl 19	. . . . . . 7 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → (𝐴 ∖ 𝐵) ≈ (𝐴 ∖ 𝐵))
31	2	ad2antrl 741	. . . . . . . . . 10 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → 𝑥 ⊆ 𝐵)
32		ssinss1 4194	. . . . . . . . . 10 ⊢ (𝑥 ⊆ 𝐵 → (𝑥 ∩ 𝐴) ⊆ 𝐵)
33	31, 32	syl 18	. . . . . . . . 9 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → (𝑥 ∩ 𝐴) ⊆ 𝐵)
34		inssdif0 4325	. . . . . . . . 9 ⊢ ((𝑥 ∩ 𝐴) ⊆ 𝐵 ↔ (𝑥 ∩ (𝐴 ∖ 𝐵)) = ∅)
35	33, 34	sylib 221	. . . . . . . 8 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → (𝑥 ∩ (𝐴 ∖ 𝐵)) = ∅)
36		disjdif 4429	. . . . . . . 8 ⊢ (𝐵 ∩ (𝐴 ∖ 𝐵)) = ∅
37	35, 36	jctir 530	. . . . . . 7 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → ((𝑥 ∩ (𝐴 ∖ 𝐵)) = ∅ ∧ (𝐵 ∩ (𝐴 ∖ 𝐵)) = ∅))
38		unen 9056	. . . . . . 7 ⊢ (((𝑥 ≈ 𝐵 ∧ (𝐴 ∖ 𝐵) ≈ (𝐴 ∖ 𝐵)) ∧ ((𝑥 ∩ (𝐴 ∖ 𝐵)) = ∅ ∧ (𝐵 ∩ (𝐴 ∖ 𝐵)) = ∅)) → (𝑥 ∪ (𝐴 ∖ 𝐵)) ≈ (𝐵 ∪ (𝐴 ∖ 𝐵)))
39	27, 30, 37, 38	syl21anc 851	. . . . . 6 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → (𝑥 ∪ (𝐴 ∖ 𝐵)) ≈ (𝐵 ∪ (𝐴 ∖ 𝐵)))
40		simplr 781	. . . . . . 7 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → 𝐵 ⊆ 𝐴)
41		undif 4441	. . . . . . 7 ⊢ (𝐵 ⊆ 𝐴 ↔ (𝐵 ∪ (𝐴 ∖ 𝐵)) = 𝐴)
42	40, 41	sylib 221	. . . . . 6 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → (𝐵 ∪ (𝐴 ∖ 𝐵)) = 𝐴)
43	39, 42	breqtrd 5135	. . . . 5 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → (𝑥 ∪ (𝐴 ∖ 𝐵)) ≈ 𝐴)
44		fin4i 10304	. . . . 5 ⊢ (((𝑥 ∪ (𝐴 ∖ 𝐵)) ⊊ 𝐴 ∧ (𝑥 ∪ (𝐴 ∖ 𝐵)) ≈ 𝐴) → ¬ 𝐴 ∈ FinIV)
45	26, 43, 44	syl2anc 596	. . . 4 ⊢ (((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) ∧ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)) → ¬ 𝐴 ∈ FinIV)
46	1, 45	pm2.65da 829	. . 3 ⊢ ((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) → ¬ (𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵))
47	46	nexdv 1969	. 2 ⊢ ((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) → ¬ ∃𝑥(𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵))
48		ssexg 5288	. . . 4 ⊢ ((𝐵 ⊆ 𝐴 ∧ 𝐴 ∈ FinIV) → 𝐵 ∈ V)
49	48	ancoms 464	. . 3 ⊢ ((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) → 𝐵 ∈ V)
50		isfin4 10303	. . 3 ⊢ (𝐵 ∈ V → (𝐵 ∈ FinIV ↔ ¬ ∃𝑥(𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)))
51	49, 50	syl 18	. 2 ⊢ ((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) → (𝐵 ∈ FinIV ↔ ¬ ∃𝑥(𝑥 ⊊ 𝐵 ∧ 𝑥 ≈ 𝐵)))
52	47, 51	mpbird 260	1 ⊢ ((𝐴 ∈ FinIV ∧ 𝐵 ⊆ 𝐴) → 𝐵 ∈ FinIV)

This proof depends on syntax axioms:  ¬ wn 3   → wi 4   ↔ wb 209   ∧ wa 401   ∨ wo 861   = wceq 1570  ∃wex 1812   ∈ wcel 2145  Vcvv 3453   ∖ cdif 3899   ∪ cun 3900   ∩ cin 3901   ⊆ wss 3902   ⊊ wpss 3903  ∅c0 4282   class class class wbr 5107   ≈ cen 8953  Fin^IVcfin4 10286

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1828  ax-4 1842  ax-5 1943  ax-6 2000  ax-7 2041  ax-8 2147  ax-9 2155  ax-12 2215  ax-ext 2734  ax-sep 5255  ax-pow 5334  ax-pr 5402  ax-un 7740

This proof depends on definitions:  df-bi 210  df-an 402  df-or 862  df-3an 1105  df-tru 1573  df-fal 1583  df-ex 1813  df-sb 2100  df-clab 2741  df-cleq 2754  df-clel 2837  df-ne 2958  df-ral 3079  df-rex 3089  df-rab 3415  df-v 3455  df-dif 3905  df-un 3907  df-in 3909  df-ss 3919  df-pss 3922  df-nul 4283  df-if 4486  df-pw 4562  df-sn 4588  df-pr 4590  df-op 4594  df-uni 4871  df-br 5108  df-opab 5172  df-id 5554  df-xp 5665  df-rel 5666  df-cnv 5667  df-co 5668  df-dm 5669  df-rn 5670  df-res 5671  df-ima 5672  df-fun 6539  df-fn 6540  df-f 6541  df-f1 6542  df-fo 6543  df-f1o 6544  df-en 8957  df-fin4 10293

This theorem is used by:  domfin4  10317