Theorem onsucf1lem 43259

Description: For ordinals, the successor operation is injective, so there is at most one ordinal that a given ordinal could be the successor of. Lemma 1.17 of [Schloeder] p. 2. (Contributed by RP, 18-Jan-2025.)

Assertion

Ref	Expression
onsucf1lem	⊢ (𝐴 ∈ On → ∃*𝑏 ∈ On 𝐴 = suc 𝑏)

Distinct variable group:   𝐴,𝑏

Proof of Theorem onsucf1lem

Dummy variable 𝑐 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		onuni 7808	. . 3 ⊢ (𝐴 ∈ On → ∪ 𝐴 ∈ On)
2		onsucuni2 7854	. . . . . . . 8 ⊢ ((𝐴 ∈ On ∧ 𝐴 = suc 𝑏) → suc ∪ 𝐴 = 𝐴)
3	2	adantlr 715	. . . . . . 7 ⊢ (((𝐴 ∈ On ∧ 𝑏 ∈ On) ∧ 𝐴 = suc 𝑏) → suc ∪ 𝐴 = 𝐴)
4		simpr 484	. . . . . . 7 ⊢ (((𝐴 ∈ On ∧ 𝑏 ∈ On) ∧ 𝐴 = suc 𝑏) → 𝐴 = suc 𝑏)
5	3, 4	eqtr2d 2776	. . . . . 6 ⊢ (((𝐴 ∈ On ∧ 𝑏 ∈ On) ∧ 𝐴 = suc 𝑏) → suc 𝑏 = suc ∪ 𝐴)
6	1	anim1i 615	. . . . . . . . 9 ⊢ ((𝐴 ∈ On ∧ 𝑏 ∈ On) → (∪ 𝐴 ∈ On ∧ 𝑏 ∈ On))
7	6	adantr 480	. . . . . . . 8 ⊢ (((𝐴 ∈ On ∧ 𝑏 ∈ On) ∧ 𝐴 = suc 𝑏) → (∪ 𝐴 ∈ On ∧ 𝑏 ∈ On))
8	7	ancomd 461	. . . . . . 7 ⊢ (((𝐴 ∈ On ∧ 𝑏 ∈ On) ∧ 𝐴 = suc 𝑏) → (𝑏 ∈ On ∧ ∪ 𝐴 ∈ On))
9		suc11 6493	. . . . . . 7 ⊢ ((𝑏 ∈ On ∧ ∪ 𝐴 ∈ On) → (suc 𝑏 = suc ∪ 𝐴 ↔ 𝑏 = ∪ 𝐴))
10	8, 9	syl 17	. . . . . 6 ⊢ (((𝐴 ∈ On ∧ 𝑏 ∈ On) ∧ 𝐴 = suc 𝑏) → (suc 𝑏 = suc ∪ 𝐴 ↔ 𝑏 = ∪ 𝐴))
11	5, 10	mpbid 232	. . . . 5 ⊢ (((𝐴 ∈ On ∧ 𝑏 ∈ On) ∧ 𝐴 = suc 𝑏) → 𝑏 = ∪ 𝐴)
12	11	ex 412	. . . 4 ⊢ ((𝐴 ∈ On ∧ 𝑏 ∈ On) → (𝐴 = suc 𝑏 → 𝑏 = ∪ 𝐴))
13	12	ralrimiva 3144	. . 3 ⊢ (𝐴 ∈ On → ∀𝑏 ∈ On (𝐴 = suc 𝑏 → 𝑏 = ∪ 𝐴))
14		eqeq2 2747	. . . . 5 ⊢ (𝑐 = ∪ 𝐴 → (𝑏 = 𝑐 ↔ 𝑏 = ∪ 𝐴))
15	14	imbi2d 340	. . . 4 ⊢ (𝑐 = ∪ 𝐴 → ((𝐴 = suc 𝑏 → 𝑏 = 𝑐) ↔ (𝐴 = suc 𝑏 → 𝑏 = ∪ 𝐴)))
16	15	ralbidv 3176	. . 3 ⊢ (𝑐 = ∪ 𝐴 → (∀𝑏 ∈ On (𝐴 = suc 𝑏 → 𝑏 = 𝑐) ↔ ∀𝑏 ∈ On (𝐴 = suc 𝑏 → 𝑏 = ∪ 𝐴)))
17	1, 13, 16	spcedv 3598	. 2 ⊢ (𝐴 ∈ On → ∃𝑐∀𝑏 ∈ On (𝐴 = suc 𝑏 → 𝑏 = 𝑐))
18		nfv 1912	. . 3 ⊢ Ⅎ𝑐 𝐴 = suc 𝑏
19	18	rmo2 3896	. 2 ⊢ (∃*𝑏 ∈ On 𝐴 = suc 𝑏 ↔ ∃𝑐∀𝑏 ∈ On (𝐴 = suc 𝑏 → 𝑏 = 𝑐))
20	17, 19	sylibr 234	1 ⊢ (𝐴 ∈ On → ∃*𝑏 ∈ On 𝐴 = suc 𝑏)

Syntax hints:   → wi 4   ↔ wb 206   ∧ wa 395   = wceq 1537  ∃wex 1776   ∈ wcel 2106  ∀wral 3059  ∃*wrmo 3377  ∪ cuni 4912  Oncon0 6386  suc csuc 6388

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1792  ax-4 1806  ax-5 1908  ax-6 1965  ax-7 2005  ax-8 2108  ax-9 2116  ax-10 2139  ax-11 2155  ax-12 2175  ax-ext 2706  ax-sep 5302  ax-nul 5312  ax-pr 5438  ax-un 7754

This theorem depends on definitions:  df-bi 207  df-an 396  df-or 848  df-3or 1087  df-3an 1088  df-tru 1540  df-fal 1550  df-ex 1777  df-nf 1781  df-sb 2063  df-mo 2538  df-clab 2713  df-cleq 2727  df-clel 2814  df-ne 2939  df-ral 3060  df-rex 3069  df-rmo 3378  df-rab 3434  df-v 3480  df-dif 3966  df-un 3968  df-in 3970  df-ss 3980  df-pss 3983  df-nul 4340  df-if 4532  df-pw 4607  df-sn 4632  df-pr 4634  df-op 4638  df-uni 4913  df-br 5149  df-opab 5211  df-tr 5266  df-eprel 5589  df-po 5597  df-so 5598  df-fr 5641  df-we 5643  df-ord 6389  df-on 6390  df-suc 6392

This theorem is referenced by:  onsucf1olem  43260