Theorem tfi 4323

Description: The Principle of Transfinite Induction. Theorem 7.17 of [TakeutiZaring] p. 39. This principle states that if 𝐴 is a class of ordinal numbers with the property that every ordinal number included in 𝐴 also belongs to 𝐴, then every ordinal number is in 𝐴.

(Contributed by NM, 18-Feb-2004.)

Assertion

Ref	Expression
tfi	⊢ ((𝐴 ⊆ On ∧ ∀𝑥 ∈ On (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴)) → 𝐴 = On)

Distinct variable group:   𝑥,𝐴

Proof of Theorem tfi

Dummy variable 𝑦 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		df-ral 2353	. . . . . . 7 ⊢ (∀𝑥 ∈ On (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴) ↔ ∀𝑥(𝑥 ∈ On → (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴)))
2		imdi 248	. . . . . . . 8 ⊢ ((𝑥 ∈ On → (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴)) ↔ ((𝑥 ∈ On → 𝑥 ⊆ 𝐴) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
3	2	albii 1399	. . . . . . 7 ⊢ (∀𝑥(𝑥 ∈ On → (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴)) ↔ ∀𝑥((𝑥 ∈ On → 𝑥 ⊆ 𝐴) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
4	1, 3	bitri 182	. . . . . 6 ⊢ (∀𝑥 ∈ On (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴) ↔ ∀𝑥((𝑥 ∈ On → 𝑥 ⊆ 𝐴) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
5		dfss2 2988	. . . . . . . . . 10 ⊢ (𝑥 ⊆ 𝐴 ↔ ∀𝑦(𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴))
6	5	imbi2i 224	. . . . . . . . 9 ⊢ ((𝑥 ∈ On → 𝑥 ⊆ 𝐴) ↔ (𝑥 ∈ On → ∀𝑦(𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)))
7		19.21v 1794	. . . . . . . . 9 ⊢ (∀𝑦(𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)) ↔ (𝑥 ∈ On → ∀𝑦(𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)))
8	6, 7	bitr4i 185	. . . . . . . 8 ⊢ ((𝑥 ∈ On → 𝑥 ⊆ 𝐴) ↔ ∀𝑦(𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)))
9	8	imbi1i 236	. . . . . . 7 ⊢ (((𝑥 ∈ On → 𝑥 ⊆ 𝐴) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) ↔ (∀𝑦(𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
10	9	albii 1399	. . . . . 6 ⊢ (∀𝑥((𝑥 ∈ On → 𝑥 ⊆ 𝐴) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) ↔ ∀𝑥(∀𝑦(𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
11	4, 10	bitri 182	. . . . 5 ⊢ (∀𝑥 ∈ On (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴) ↔ ∀𝑥(∀𝑦(𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
12		simpl 107	. . . . . . . . . . 11 ⊢ ((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → 𝑦 ∈ 𝑥)
13		tron 4137	. . . . . . . . . . . . . 14 ⊢ Tr On
14		dftr2 3877	. . . . . . . . . . . . . 14 ⊢ (Tr On ↔ ∀𝑦∀𝑥((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → 𝑦 ∈ On))
15	13, 14	mpbi 143	. . . . . . . . . . . . 13 ⊢ ∀𝑦∀𝑥((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → 𝑦 ∈ On)
16	15	spi 1469	. . . . . . . . . . . 12 ⊢ ∀𝑥((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → 𝑦 ∈ On)
17	16	spi 1469	. . . . . . . . . . 11 ⊢ ((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → 𝑦 ∈ On)
18	12, 17	jca 300	. . . . . . . . . 10 ⊢ ((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → (𝑦 ∈ 𝑥 ∧ 𝑦 ∈ On))
19	18	imim1i 59	. . . . . . . . 9 ⊢ (((𝑦 ∈ 𝑥 ∧ 𝑦 ∈ On) → 𝑦 ∈ 𝐴) → ((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → 𝑦 ∈ 𝐴))
20		impexp 259	. . . . . . . . 9 ⊢ (((𝑦 ∈ 𝑥 ∧ 𝑦 ∈ On) → 𝑦 ∈ 𝐴) ↔ (𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)))
21		impexp 259	. . . . . . . . . 10 ⊢ (((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → 𝑦 ∈ 𝐴) ↔ (𝑦 ∈ 𝑥 → (𝑥 ∈ On → 𝑦 ∈ 𝐴)))
22		bi2.04 246	. . . . . . . . . 10 ⊢ ((𝑦 ∈ 𝑥 → (𝑥 ∈ On → 𝑦 ∈ 𝐴)) ↔ (𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)))
23	21, 22	bitri 182	. . . . . . . . 9 ⊢ (((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ On) → 𝑦 ∈ 𝐴) ↔ (𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)))
24	19, 20, 23	3imtr3i 198	. . . . . . . 8 ⊢ ((𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)))
25	24	alimi 1384	. . . . . . 7 ⊢ (∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → ∀𝑦(𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)))
26	25	imim1i 59	. . . . . 6 ⊢ ((∀𝑦(𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) → (∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
27	26	alimi 1384	. . . . 5 ⊢ (∀𝑥(∀𝑦(𝑥 ∈ On → (𝑦 ∈ 𝑥 → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) → ∀𝑥(∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
28	11, 27	sylbi 119	. . . 4 ⊢ (∀𝑥 ∈ On (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴) → ∀𝑥(∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
29	28	adantl 271	. . 3 ⊢ ((𝐴 ⊆ On ∧ ∀𝑥 ∈ On (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴)) → ∀𝑥(∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
30		sbim 1868	. . . . . . . . . 10 ⊢ ([𝑦 / 𝑥](𝑥 ∈ On → 𝑥 ∈ 𝐴) ↔ ([𝑦 / 𝑥]𝑥 ∈ On → [𝑦 / 𝑥]𝑥 ∈ 𝐴))
31		clelsb3 2183	. . . . . . . . . . 11 ⊢ ([𝑦 / 𝑥]𝑥 ∈ On ↔ 𝑦 ∈ On)
32		clelsb3 2183	. . . . . . . . . . 11 ⊢ ([𝑦 / 𝑥]𝑥 ∈ 𝐴 ↔ 𝑦 ∈ 𝐴)
33	31, 32	imbi12i 237	. . . . . . . . . 10 ⊢ (([𝑦 / 𝑥]𝑥 ∈ On → [𝑦 / 𝑥]𝑥 ∈ 𝐴) ↔ (𝑦 ∈ On → 𝑦 ∈ 𝐴))
34	30, 33	bitri 182	. . . . . . . . 9 ⊢ ([𝑦 / 𝑥](𝑥 ∈ On → 𝑥 ∈ 𝐴) ↔ (𝑦 ∈ On → 𝑦 ∈ 𝐴))
35	34	ralbii 2372	. . . . . . . 8 ⊢ (∀𝑦 ∈ 𝑥 [𝑦 / 𝑥](𝑥 ∈ On → 𝑥 ∈ 𝐴) ↔ ∀𝑦 ∈ 𝑥 (𝑦 ∈ On → 𝑦 ∈ 𝐴))
36		df-ral 2353	. . . . . . . 8 ⊢ (∀𝑦 ∈ 𝑥 (𝑦 ∈ On → 𝑦 ∈ 𝐴) ↔ ∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)))
37	35, 36	bitri 182	. . . . . . 7 ⊢ (∀𝑦 ∈ 𝑥 [𝑦 / 𝑥](𝑥 ∈ On → 𝑥 ∈ 𝐴) ↔ ∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)))
38	37	imbi1i 236	. . . . . 6 ⊢ ((∀𝑦 ∈ 𝑥 [𝑦 / 𝑥](𝑥 ∈ On → 𝑥 ∈ 𝐴) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) ↔ (∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
39	38	albii 1399	. . . . 5 ⊢ (∀𝑥(∀𝑦 ∈ 𝑥 [𝑦 / 𝑥](𝑥 ∈ On → 𝑥 ∈ 𝐴) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) ↔ ∀𝑥(∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)))
40		ax-setind 4280	. . . . 5 ⊢ (∀𝑥(∀𝑦 ∈ 𝑥 [𝑦 / 𝑥](𝑥 ∈ On → 𝑥 ∈ 𝐴) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) → ∀𝑥(𝑥 ∈ On → 𝑥 ∈ 𝐴))
41	39, 40	sylbir 133	. . . 4 ⊢ (∀𝑥(∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) → ∀𝑥(𝑥 ∈ On → 𝑥 ∈ 𝐴))
42		dfss2 2988	. . . 4 ⊢ (On ⊆ 𝐴 ↔ ∀𝑥(𝑥 ∈ On → 𝑥 ∈ 𝐴))
43	41, 42	sylibr 132	. . 3 ⊢ (∀𝑥(∀𝑦(𝑦 ∈ 𝑥 → (𝑦 ∈ On → 𝑦 ∈ 𝐴)) → (𝑥 ∈ On → 𝑥 ∈ 𝐴)) → On ⊆ 𝐴)
44	29, 43	syl 14	. 2 ⊢ ((𝐴 ⊆ On ∧ ∀𝑥 ∈ On (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴)) → On ⊆ 𝐴)
45		eqss 3014	. . 3 ⊢ (𝐴 = On ↔ (𝐴 ⊆ On ∧ On ⊆ 𝐴))
46	45	biimpri 131	. 2 ⊢ ((𝐴 ⊆ On ∧ On ⊆ 𝐴) → 𝐴 = On)
47	44, 46	syldan 276	1 ⊢ ((𝐴 ⊆ On ∧ ∀𝑥 ∈ On (𝑥 ⊆ 𝐴 → 𝑥 ∈ 𝐴)) → 𝐴 = On)

Syntax hints:   → wi 4   ∧ wa 102  ∀wal 1282   = wceq 1284   ∈ wcel 1433  [wsb 1685  ∀wral 2348   ⊆ wss 2973  Tr wtr 3875  Oncon0 4118

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-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  ax-setind 4280

This theorem depends on definitions:  df-bi 115  df-3an 921  df-tru 1287  df-nf 1390  df-sb 1686  df-clab 2068  df-cleq 2074  df-clel 2077  df-nfc 2208  df-ral 2353  df-rex 2354  df-v 2603  df-in 2979  df-ss 2986  df-uni 3602  df-tr 3876  df-iord 4121  df-on 4123

This theorem is referenced by:  tfis  4324