Theorem nninfisol 7424

Description: Finite elements of ℕ_∞ are isolated. That is, given a natural number and any element of ℕ_∞, it is decidable whether the natural number (when converted to an element of ℕ_∞) is equal to the given element of ℕ_∞. Stated in an online post by Martin Escardo. One way to understand this theorem is that you do not need to look at an unbounded number of elements of the sequence 𝑋 to decide whether it is equal to 𝑁 (in fact, you only need to look at two elements and 𝑁 tells you where to look).

By contrast, the point at infinity being isolated is equivalent to the Weak Limited Principle of Omniscience (WLPO) (nninfinfwlpo 7471). (Contributed by BJ and Jim Kingdon, 12-Sep-2024.)

Assertion

Ref	Expression
nninfisol	⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)

Distinct variable groups:   𝑖,𝑁   𝑖,𝑋

Proof of Theorem nninfisol

Step	Hyp	Ref	Expression
1		simpllr 536	. . . 4 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ 𝑁 = ∅) → 𝑋 ∈ ℕ∞)
2		simplr 529	. . . 4 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ 𝑁 = ∅) → (𝑋‘𝑁) = ∅)
3		simplll 535	. . . 4 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ 𝑁 = ∅) → 𝑁 ∈ ω)
4		simpr 110	. . . 4 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ 𝑁 = ∅) → 𝑁 = ∅)
5	1, 2, 3, 4	nninfisollem0 7421	. . 3 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ 𝑁 = ∅) → DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)
6		simp-4r 544	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = ∅) → 𝑋 ∈ ℕ∞)
7		simpllr 536	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = ∅) → (𝑋‘𝑁) = ∅)
8		simp-4l 543	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = ∅) → 𝑁 ∈ ω)
9		simpr 110	. . . . . . 7 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) → ¬ 𝑁 = ∅)
10	9	neqned 2419	. . . . . 6 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) → 𝑁 ≠ ∅)
11	10	adantr 276	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = ∅) → 𝑁 ≠ ∅)
12		simpr 110	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = ∅) → (𝑋‘∪ 𝑁) = ∅)
13	6, 7, 8, 11, 12	nninfisollemne 7422	. . . 4 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = ∅) → DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)
14		simp-4r 544	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = 1o) → 𝑋 ∈ ℕ∞)
15		simpllr 536	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = 1o) → (𝑋‘𝑁) = ∅)
16		simp-4l 543	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = 1o) → 𝑁 ∈ ω)
17	10	adantr 276	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = 1o) → 𝑁 ≠ ∅)
18		simpr 110	. . . . 5 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = 1o) → (𝑋‘∪ 𝑁) = 1o)
19	14, 15, 16, 17, 18	nninfisollemeq 7423	. . . 4 ⊢ (((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) ∧ (𝑋‘∪ 𝑁) = 1o) → DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)
20		nninff 7413	. . . . . . . . 9 ⊢ (𝑋 ∈ ℕ∞ → 𝑋:ω⟶2o)
21	20	adantl 277	. . . . . . . 8 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → 𝑋:ω⟶2o)
22		nnpredcl 4745	. . . . . . . . 9 ⊢ (𝑁 ∈ ω → ∪ 𝑁 ∈ ω)
23	22	adantr 276	. . . . . . . 8 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → ∪ 𝑁 ∈ ω)
24	21, 23	ffvelcdmd 5813	. . . . . . 7 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → (𝑋‘∪ 𝑁) ∈ 2o)
25		df2o3 6662	. . . . . . 7 ⊢ 2o = {∅, 1o}
26	24, 25	eleqtrdi 2325	. . . . . 6 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → (𝑋‘∪ 𝑁) ∈ {∅, 1o})
27		elpri 3712	. . . . . 6 ⊢ ((𝑋‘∪ 𝑁) ∈ {∅, 1o} → ((𝑋‘∪ 𝑁) = ∅ ∨ (𝑋‘∪ 𝑁) = 1o))
28	26, 27	syl 14	. . . . 5 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → ((𝑋‘∪ 𝑁) = ∅ ∨ (𝑋‘∪ 𝑁) = 1o))
29	28	ad2antrr 488	. . . 4 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) → ((𝑋‘∪ 𝑁) = ∅ ∨ (𝑋‘∪ 𝑁) = 1o))
30	13, 19, 29	mpjaodan 806	. . 3 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) ∧ ¬ 𝑁 = ∅) → DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)
31		nndceq0 4740	. . . . 5 ⊢ (𝑁 ∈ ω → DECID 𝑁 = ∅)
32		exmiddc 844	. . . . 5 ⊢ (DECID 𝑁 = ∅ → (𝑁 = ∅ ∨ ¬ 𝑁 = ∅))
33	31, 32	syl 14	. . . 4 ⊢ (𝑁 ∈ ω → (𝑁 = ∅ ∨ ¬ 𝑁 = ∅))
34	33	ad2antrr 488	. . 3 ⊢ (((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) → (𝑁 = ∅ ∨ ¬ 𝑁 = ∅))
35	5, 30, 34	mpjaodan 806	. 2 ⊢ (((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = ∅) → DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)
36		1n0 6665	. . . . . 6 ⊢ 1o ≠ ∅
37	36	neii 2414	. . . . 5 ⊢ ¬ 1o = ∅
38		simpr 110	. . . . . . . 8 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) ∧ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋) → (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)
39	38	fveq1d 5672	. . . . . . 7 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) ∧ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋) → ((𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅))‘𝑁) = (𝑋‘𝑁))
40		eqid 2232	. . . . . . . . . 10 ⊢ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅))
41		eleq1 2295	. . . . . . . . . . 11 ⊢ (𝑖 = 𝑁 → (𝑖 ∈ 𝑁 ↔ 𝑁 ∈ 𝑁))
42	41	ifbid 3644	. . . . . . . . . 10 ⊢ (𝑖 = 𝑁 → if(𝑖 ∈ 𝑁, 1o, ∅) = if(𝑁 ∈ 𝑁, 1o, ∅))
43		id 19	. . . . . . . . . 10 ⊢ (𝑁 ∈ ω → 𝑁 ∈ ω)
44		nnord 4734	. . . . . . . . . . . . 13 ⊢ (𝑁 ∈ ω → Ord 𝑁)
45		ordirr 4664	. . . . . . . . . . . . 13 ⊢ (Ord 𝑁 → ¬ 𝑁 ∈ 𝑁)
46	44, 45	syl 14	. . . . . . . . . . . 12 ⊢ (𝑁 ∈ ω → ¬ 𝑁 ∈ 𝑁)
47	46	iffalsed 3632	. . . . . . . . . . 11 ⊢ (𝑁 ∈ ω → if(𝑁 ∈ 𝑁, 1o, ∅) = ∅)
48		peano1 4716	. . . . . . . . . . 11 ⊢ ∅ ∈ ω
49	47, 48	eqeltrdi 2323	. . . . . . . . . 10 ⊢ (𝑁 ∈ ω → if(𝑁 ∈ 𝑁, 1o, ∅) ∈ ω)
50	40, 42, 43, 49	fvmptd3 5771	. . . . . . . . 9 ⊢ (𝑁 ∈ ω → ((𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅))‘𝑁) = if(𝑁 ∈ 𝑁, 1o, ∅))
51	50, 47	eqtrd 2265	. . . . . . . 8 ⊢ (𝑁 ∈ ω → ((𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅))‘𝑁) = ∅)
52	51	ad3antrrr 492	. . . . . . 7 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) ∧ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋) → ((𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅))‘𝑁) = ∅)
53		simplr 529	. . . . . . 7 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) ∧ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋) → (𝑋‘𝑁) = 1o)
54	39, 52, 53	3eqtr3rd 2274	. . . . . 6 ⊢ ((((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) ∧ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋) → 1o = ∅)
55	54	ex 115	. . . . 5 ⊢ (((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) → ((𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋 → 1o = ∅))
56	37, 55	mtoi 670	. . . 4 ⊢ (((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) → ¬ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)
57	56	olcd 742	. . 3 ⊢ (((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) → ((𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋 ∨ ¬ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋))
58		df-dc 843	. . 3 ⊢ (DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋 ↔ ((𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋 ∨ ¬ (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋))
59	57, 58	sylibr 134	. 2 ⊢ (((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) ∧ (𝑋‘𝑁) = 1o) → DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)
60		simpl 109	. . . . 5 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → 𝑁 ∈ ω)
61	21, 60	ffvelcdmd 5813	. . . 4 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → (𝑋‘𝑁) ∈ 2o)
62	61, 25	eleqtrdi 2325	. . 3 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → (𝑋‘𝑁) ∈ {∅, 1o})
63		elpri 3712	. . 3 ⊢ ((𝑋‘𝑁) ∈ {∅, 1o} → ((𝑋‘𝑁) = ∅ ∨ (𝑋‘𝑁) = 1o))
64	62, 63	syl 14	. 2 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → ((𝑋‘𝑁) = ∅ ∨ (𝑋‘𝑁) = 1o))
65	35, 59, 64	mpjaodan 806	1 ⊢ ((𝑁 ∈ ω ∧ 𝑋 ∈ ℕ∞) → DECID (𝑖 ∈ ω ↦ if(𝑖 ∈ 𝑁, 1o, ∅)) = 𝑋)

Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 104   ∨ wo 716  DECID wdc 842   = wceq 1398   ∈ wcel 2203   ≠ wne 2412  ∅c0 3508  ifcif 3620  {cpr 3690  ∪ cuni 3914   ↦ cmpt 4171  Ord word 4483  ωcom 4712  ⟶wf 5348  ‘cfv 5352  1_oc1o 6640  2_oc2o 6641  ℕ_∞xnninf 7410

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 619  ax-in2 620  ax-io 717  ax-5 1496  ax-7 1497  ax-gen 1498  ax-ie1 1542  ax-ie2 1543  ax-8 1553  ax-10 1554  ax-11 1555  ax-i12 1556  ax-bndl 1558  ax-4 1559  ax-17 1575  ax-i9 1579  ax-ial 1583  ax-i5r 1584  ax-13 2205  ax-14 2206  ax-ext 2214  ax-sep 4228  ax-nul 4236  ax-pow 4287  ax-pr 4322  ax-un 4554  ax-setind 4659  ax-iinf 4710

This theorem depends on definitions:  df-bi 117  df-dc 843  df-3or 1006  df-3an 1007  df-tru 1401  df-fal 1404  df-nf 1510  df-sb 1812  df-eu 2083  df-mo 2084  df-clab 2219  df-cleq 2225  df-clel 2228  df-nfc 2373  df-ne 2413  df-ral 2525  df-rex 2526  df-rab 2529  df-v 2815  df-sbc 3043  df-csb 3139  df-dif 3213  df-un 3215  df-in 3217  df-ss 3224  df-nul 3509  df-if 3621  df-pw 3671  df-sn 3695  df-pr 3696  df-op 3698  df-uni 3915  df-int 3950  df-br 4110  df-opab 4172  df-mpt 4173  df-tr 4209  df-id 4414  df-iord 4487  df-on 4489  df-suc 4492  df-iom 4713  df-xp 4755  df-rel 4756  df-cnv 4757  df-co 4758  df-dm 4759  df-rn 4760  df-iota 5312  df-fun 5354  df-fn 5355  df-f 5356  df-fv 5360  df-ov 6053  df-oprab 6054  df-mpo 6055  df-1o 6647  df-2o 6648  df-map 6884  df-nninf 7411

This theorem is referenced by: (None)