Theorem rmoeqALT 28711

Description: Equality's restricted existential "at most one" property. (Contributed by Thierry Arnoux, 30-Mar-2018.) Obsolete version of rmoeq 3372 as of 27-Oct-2020. (New usage is discouraged.) (Proof modification is discouraged.)

Assertion

Ref	Expression
rmoeqALT	⊢ (𝐴 ∈ 𝑉 → ∃*𝑥 ∈ 𝐵 𝑥 = 𝐴)

Distinct variable groups:   𝑥,𝐴   𝑥,𝐵

Allowed substitution hint:   𝑉(𝑥)

Proof of Theorem rmoeqALT

Dummy variable 𝑦 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		id 22	. . . 4 ⊢ (𝑥 = 𝐴 → 𝑥 = 𝐴)
2	1	rgenw 2908	. . 3 ⊢ ∀𝑥 ∈ 𝐵 (𝑥 = 𝐴 → 𝑥 = 𝐴)
3		eqeq2 2621	. . . . . 6 ⊢ (𝑦 = 𝐴 → (𝑥 = 𝑦 ↔ 𝑥 = 𝐴))
4	3	imbi2d 329	. . . . 5 ⊢ (𝑦 = 𝐴 → ((𝑥 = 𝐴 → 𝑥 = 𝑦) ↔ (𝑥 = 𝐴 → 𝑥 = 𝐴)))
5	4	ralbidv 2969	. . . 4 ⊢ (𝑦 = 𝐴 → (∀𝑥 ∈ 𝐵 (𝑥 = 𝐴 → 𝑥 = 𝑦) ↔ ∀𝑥 ∈ 𝐵 (𝑥 = 𝐴 → 𝑥 = 𝐴)))
6	5	spcegv 3267	. . 3 ⊢ (𝐴 ∈ 𝑉 → (∀𝑥 ∈ 𝐵 (𝑥 = 𝐴 → 𝑥 = 𝐴) → ∃𝑦∀𝑥 ∈ 𝐵 (𝑥 = 𝐴 → 𝑥 = 𝑦)))
7	2, 6	mpi 20	. 2 ⊢ (𝐴 ∈ 𝑉 → ∃𝑦∀𝑥 ∈ 𝐵 (𝑥 = 𝐴 → 𝑥 = 𝑦))
8		nfv 1830	. . 3 ⊢ Ⅎ𝑦 𝑥 = 𝐴
9	8	rmo2 3492	. 2 ⊢ (∃*𝑥 ∈ 𝐵 𝑥 = 𝐴 ↔ ∃𝑦∀𝑥 ∈ 𝐵 (𝑥 = 𝐴 → 𝑥 = 𝑦))
10	7, 9	sylibr 223	1 ⊢ (𝐴 ∈ 𝑉 → ∃*𝑥 ∈ 𝐵 𝑥 = 𝐴)

Syntax hints:   → wi 4   = wceq 1475  ∃wex 1695   ∈ wcel 1977  ∀wral 2896  ∃*wrmo 2899

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1713  ax-4 1728  ax-5 1827  ax-6 1875  ax-7 1922  ax-10 2006  ax-11 2021  ax-12 2034  ax-13 2234  ax-ext 2590

This theorem depends on definitions:  df-bi 196  df-or 384  df-an 385  df-tru 1478  df-ex 1696  df-nf 1701  df-sb 1868  df-eu 2462  df-mo 2463  df-clab 2597  df-cleq 2603  df-clel 2606  df-nfc 2740  df-ral 2901  df-rmo 2904  df-v 3175

This theorem is referenced by: (None)