Theorem en1bg 6303

Description: A set is equinumerous to ordinal one iff it is a singleton. (Contributed by Jim Kingdon, 13-Apr-2020.)

Assertion

Ref	Expression
en1bg	⊢ (𝐴 ∈ 𝑉 → (𝐴 ≈ 1𝑜 ↔ 𝐴 = {∪ 𝐴}))

Proof of Theorem en1bg

Dummy variable 𝑥 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		en1 6302	. . 3 ⊢ (𝐴 ≈ 1𝑜 ↔ ∃𝑥 𝐴 = {𝑥})
2		id 19	. . . . 5 ⊢ (𝐴 = {𝑥} → 𝐴 = {𝑥})
3		unieq 3610	. . . . . . 7 ⊢ (𝐴 = {𝑥} → ∪ 𝐴 = ∪ {𝑥})
4		vex 2604	. . . . . . . 8 ⊢ 𝑥 ∈ V
5	4	unisn 3617	. . . . . . 7 ⊢ ∪ {𝑥} = 𝑥
6	3, 5	syl6eq 2129	. . . . . 6 ⊢ (𝐴 = {𝑥} → ∪ 𝐴 = 𝑥)
7	6	sneqd 3411	. . . . 5 ⊢ (𝐴 = {𝑥} → {∪ 𝐴} = {𝑥})
8	2, 7	eqtr4d 2116	. . . 4 ⊢ (𝐴 = {𝑥} → 𝐴 = {∪ 𝐴})
9	8	exlimiv 1529	. . 3 ⊢ (∃𝑥 𝐴 = {𝑥} → 𝐴 = {∪ 𝐴})
10	1, 9	sylbi 119	. 2 ⊢ (𝐴 ≈ 1𝑜 → 𝐴 = {∪ 𝐴})
11		uniexg 4193	. . . 4 ⊢ (𝐴 ∈ 𝑉 → ∪ 𝐴 ∈ V)
12		ensn1g 6300	. . . 4 ⊢ (∪ 𝐴 ∈ V → {∪ 𝐴} ≈ 1𝑜)
13	11, 12	syl 14	. . 3 ⊢ (𝐴 ∈ 𝑉 → {∪ 𝐴} ≈ 1𝑜)
14		breq1 3788	. . 3 ⊢ (𝐴 = {∪ 𝐴} → (𝐴 ≈ 1𝑜 ↔ {∪ 𝐴} ≈ 1𝑜))
15	13, 14	syl5ibrcom 155	. 2 ⊢ (𝐴 ∈ 𝑉 → (𝐴 = {∪ 𝐴} → 𝐴 ≈ 1𝑜))
16	10, 15	impbid2 141	1 ⊢ (𝐴 ∈ 𝑉 → (𝐴 ≈ 1𝑜 ↔ 𝐴 = {∪ 𝐴}))

Syntax hints:   → wi 4   ↔ wb 103   = wceq 1284  ∃wex 1421   ∈ wcel 1433  Vcvv 2601  {csn 3398  ∪ cuni 3601   class class class wbr 3785  1_𝑜c1o 6017   ≈ cen 6242

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-in1 576  ax-in2 577  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-13 1444  ax-14 1445  ax-17 1459  ax-i9 1463  ax-ial 1467  ax-i5r 1468  ax-ext 2063  ax-sep 3896  ax-nul 3904  ax-pow 3948  ax-pr 3964  ax-un 4188

This theorem depends on definitions:  df-bi 115  df-3an 921  df-tru 1287  df-nf 1390  df-sb 1686  df-eu 1944  df-mo 1945  df-clab 2068  df-cleq 2074  df-clel 2077  df-nfc 2208  df-ral 2353  df-rex 2354  df-reu 2355  df-v 2603  df-sbc 2816  df-dif 2975  df-un 2977  df-in 2979  df-ss 2986  df-nul 3252  df-pw 3384  df-sn 3404  df-pr 3405  df-op 3407  df-uni 3602  df-br 3786  df-opab 3840  df-id 4048  df-suc 4126  df-xp 4369  df-rel 4370  df-cnv 4371  df-co 4372  df-dm 4373  df-rn 4374  df-res 4375  df-ima 4376  df-iota 4887  df-fun 4924  df-fn 4925  df-f 4926  df-f1 4927  df-fo 4928  df-f1o 4929  df-fv 4930  df-1o 6024  df-en 6245

This theorem is referenced by:  en1uniel  6307