Theorem dfid2 5533

Description: Alternate definition of the identity relation. Instance of dfid3 5534 not requiring auxiliary axioms. (Contributed by NM, 15-Mar-2007.) Reduce axiom usage. (Revised by Gino Giotto, 4-Nov-2024.) (Proof shortened by BJ, 5-Nov-2024.)

Use df-id 5531 instead to make the semantics of the constructor df-opab 5168 clearer. (New usage is discouraged.)

Assertion

Ref	Expression
dfid2	⊢ I = {⟨𝑥, 𝑥⟩ ∣ 𝑥 = 𝑥}

Proof of Theorem dfid2

Dummy variables 𝑦 𝑧 𝑢 are mutually distinct and distinct from all other variables.

Step	Hyp	Ref	Expression
1		df-id 5531	. 2 ⊢ I = {⟨𝑥, 𝑦⟩ ∣ 𝑥 = 𝑦}
2		equcomi 2020	. . . . . . . . . . . 12 ⊢ (𝑥 = 𝑦 → 𝑦 = 𝑥)
3	2	opeq2d 4837	. . . . . . . . . . 11 ⊢ (𝑥 = 𝑦 → ⟨𝑥, 𝑦⟩ = ⟨𝑥, 𝑥⟩)
4	3	eqeq2d 2747	. . . . . . . . . 10 ⊢ (𝑥 = 𝑦 → (𝑧 = ⟨𝑥, 𝑦⟩ ↔ 𝑧 = ⟨𝑥, 𝑥⟩))
5	4	pm5.32ri 576	. . . . . . . . 9 ⊢ ((𝑧 = ⟨𝑥, 𝑦⟩ ∧ 𝑥 = 𝑦) ↔ (𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑦))
6	5	exbii 1850	. . . . . . . 8 ⊢ (∃𝑦(𝑧 = ⟨𝑥, 𝑦⟩ ∧ 𝑥 = 𝑦) ↔ ∃𝑦(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑦))
7		ax6evr 2018	. . . . . . . . 9 ⊢ ∃𝑦 𝑥 = 𝑦
8		19.42v 1957	. . . . . . . . 9 ⊢ (∃𝑦(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑦) ↔ (𝑧 = ⟨𝑥, 𝑥⟩ ∧ ∃𝑦 𝑥 = 𝑦))
9	7, 8	mpbiran2 708	. . . . . . . 8 ⊢ (∃𝑦(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑦) ↔ 𝑧 = ⟨𝑥, 𝑥⟩)
10	6, 9	bitri 274	. . . . . . 7 ⊢ (∃𝑦(𝑧 = ⟨𝑥, 𝑦⟩ ∧ 𝑥 = 𝑦) ↔ 𝑧 = ⟨𝑥, 𝑥⟩)
11		eqidd 2737	. . . . . . . 8 ⊢ (𝑧 = ⟨𝑥, 𝑥⟩ → 𝑥 = 𝑥)
12	11	pm4.71i 560	. . . . . . 7 ⊢ (𝑧 = ⟨𝑥, 𝑥⟩ ↔ (𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥))
13	10, 12	bitri 274	. . . . . 6 ⊢ (∃𝑦(𝑧 = ⟨𝑥, 𝑦⟩ ∧ 𝑥 = 𝑦) ↔ (𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥))
14	13	exbii 1850	. . . . 5 ⊢ (∃𝑥∃𝑦(𝑧 = ⟨𝑥, 𝑦⟩ ∧ 𝑥 = 𝑦) ↔ ∃𝑥(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥))
15		id 22	. . . . . . . . 9 ⊢ (𝑥 = 𝑢 → 𝑥 = 𝑢)
16	15, 15	opeq12d 4838	. . . . . . . 8 ⊢ (𝑥 = 𝑢 → ⟨𝑥, 𝑥⟩ = ⟨𝑢, 𝑢⟩)
17	16	eqeq2d 2747	. . . . . . 7 ⊢ (𝑥 = 𝑢 → (𝑧 = ⟨𝑥, 𝑥⟩ ↔ 𝑧 = ⟨𝑢, 𝑢⟩))
18	15, 15	eqeq12d 2752	. . . . . . 7 ⊢ (𝑥 = 𝑢 → (𝑥 = 𝑥 ↔ 𝑢 = 𝑢))
19	17, 18	anbi12d 631	. . . . . 6 ⊢ (𝑥 = 𝑢 → ((𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥) ↔ (𝑧 = ⟨𝑢, 𝑢⟩ ∧ 𝑢 = 𝑢)))
20	19	exexw 2054	. . . . 5 ⊢ (∃𝑥(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥) ↔ ∃𝑥∃𝑥(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥))
21	14, 20	bitri 274	. . . 4 ⊢ (∃𝑥∃𝑦(𝑧 = ⟨𝑥, 𝑦⟩ ∧ 𝑥 = 𝑦) ↔ ∃𝑥∃𝑥(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥))
22	21	abbii 2806	. . 3 ⊢ {𝑧 ∣ ∃𝑥∃𝑦(𝑧 = ⟨𝑥, 𝑦⟩ ∧ 𝑥 = 𝑦)} = {𝑧 ∣ ∃𝑥∃𝑥(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥)}
23		df-opab 5168	. . 3 ⊢ {⟨𝑥, 𝑦⟩ ∣ 𝑥 = 𝑦} = {𝑧 ∣ ∃𝑥∃𝑦(𝑧 = ⟨𝑥, 𝑦⟩ ∧ 𝑥 = 𝑦)}
24		df-opab 5168	. . 3 ⊢ {⟨𝑥, 𝑥⟩ ∣ 𝑥 = 𝑥} = {𝑧 ∣ ∃𝑥∃𝑥(𝑧 = ⟨𝑥, 𝑥⟩ ∧ 𝑥 = 𝑥)}
25	22, 23, 24	3eqtr4i 2774	. 2 ⊢ {⟨𝑥, 𝑦⟩ ∣ 𝑥 = 𝑦} = {⟨𝑥, 𝑥⟩ ∣ 𝑥 = 𝑥}
26	1, 25	eqtri 2764	1 ⊢ I = {⟨𝑥, 𝑥⟩ ∣ 𝑥 = 𝑥}

Syntax hints:   ∧ wa 396   = wceq 1541  ∃wex 1781  {cab 2713  ⟨cop 4592  {copab 5167   I cid 5530

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1913  ax-6 1971  ax-7 2011  ax-8 2108  ax-9 2116  ax-ext 2707

This theorem depends on definitions:  df-bi 206  df-an 397  df-or 846  df-3an 1089  df-tru 1544  df-fal 1554  df-ex 1782  df-sb 2068  df-clab 2714  df-cleq 2728  df-clel 2814  df-rab 3408  df-v 3447  df-dif 3913  df-un 3915  df-in 3917  df-ss 3927  df-nul 4283  df-if 4487  df-sn 4587  df-pr 4589  df-op 4593  df-opab 5168  df-id 5531

This theorem is referenced by: (None)