Theorem en1 7090

Description: A set is equinumerous to ordinal one iff it is a singleton. (Contributed by NM, 25-Jul-2004.)

Assertion

Ref	Expression
en1	⊢ (𝐴 ≈ 1o ↔ ∃𝑥 𝐴 = {𝑥})

Distinct variable group:   𝑥,𝐴

Proof of Theorem en1

Dummy variable 𝑓 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		df1o2 6705	. . . . 5 ⊢ 1o = {∅}
2	1	breq2i 4139	. . . 4 ⊢ (𝐴 ≈ 1o ↔ 𝐴 ≈ {∅})
3		bren 7034	. . . 4 ⊢ (𝐴 ≈ {∅} ↔ ∃𝑓 𝑓:𝐴–1-1-onto→{∅})
4	2, 3	bitri 184	. . 3 ⊢ (𝐴 ≈ 1o ↔ ∃𝑓 𝑓:𝐴–1-1-onto→{∅})
5		f1ocnv 5655	. . . . 5 ⊢ (𝑓:𝐴–1-1-onto→{∅} → ◡𝑓:{∅}–1-1-onto→𝐴)
6		f1ofo 5649	. . . . . . . 8 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → ◡𝑓:{∅}–onto→𝐴)
7		forn 5621	. . . . . . . 8 ⊢ (◡𝑓:{∅}–onto→𝐴 → ran ◡𝑓 = 𝐴)
8	6, 7	syl 14	. . . . . . 7 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → ran ◡𝑓 = 𝐴)
9		f1of 5642	. . . . . . . . . 10 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → ◡𝑓:{∅}⟶𝐴)
10		0ex 4262	. . . . . . . . . . . 12 ⊢ ∅ ∈ V
11	10	fsn2 5885	. . . . . . . . . . 11 ⊢ (◡𝑓:{∅}⟶𝐴 ↔ ((◡𝑓‘∅) ∈ 𝐴 ∧ ◡𝑓 = {⟨∅, (◡𝑓‘∅)⟩}))
12	11	simprbi 275	. . . . . . . . . 10 ⊢ (◡𝑓:{∅}⟶𝐴 → ◡𝑓 = {⟨∅, (◡𝑓‘∅)⟩})
13	9, 12	syl 14	. . . . . . . . 9 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → ◡𝑓 = {⟨∅, (◡𝑓‘∅)⟩})
14	13	rneqd 5013	. . . . . . . 8 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → ran ◡𝑓 = ran {⟨∅, (◡𝑓‘∅)⟩})
15	10	rnsnop 5271	. . . . . . . 8 ⊢ ran {⟨∅, (◡𝑓‘∅)⟩} = {(◡𝑓‘∅)}
16	14, 15	eqtrdi 2287	. . . . . . 7 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → ran ◡𝑓 = {(◡𝑓‘∅)})
17	8, 16	eqtr3d 2273	. . . . . 6 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → 𝐴 = {(◡𝑓‘∅)})
18	5, 17	syl 14	. . . . 5 ⊢ (𝑓:𝐴–1-1-onto→{∅} → 𝐴 = {(◡𝑓‘∅)})
19		f1ofn 5643	. . . . . . 7 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → ◡𝑓 Fn {∅})
20	10	snid 3740	. . . . . . 7 ⊢ ∅ ∈ {∅}
21		funfvex 5715	. . . . . . . 8 ⊢ ((Fun ◡𝑓 ∧ ∅ ∈ dom ◡𝑓) → (◡𝑓‘∅) ∈ V)
22	21	funfni 5486	. . . . . . 7 ⊢ ((◡𝑓 Fn {∅} ∧ ∅ ∈ {∅}) → (◡𝑓‘∅) ∈ V)
23	19, 20, 22	sylancl 417	. . . . . 6 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → (◡𝑓‘∅) ∈ V)
24		sneq 3720	. . . . . . . 8 ⊢ (𝑥 = (◡𝑓‘∅) → {𝑥} = {(◡𝑓‘∅)})
25	24	eqeq2d 2250	. . . . . . 7 ⊢ (𝑥 = (◡𝑓‘∅) → (𝐴 = {𝑥} ↔ 𝐴 = {(◡𝑓‘∅)}))
26	25	spcegv 2913	. . . . . 6 ⊢ ((◡𝑓‘∅) ∈ V → (𝐴 = {(◡𝑓‘∅)} → ∃𝑥 𝐴 = {𝑥}))
27	23, 26	syl 14	. . . . 5 ⊢ (◡𝑓:{∅}–1-1-onto→𝐴 → (𝐴 = {(◡𝑓‘∅)} → ∃𝑥 𝐴 = {𝑥}))
28	5, 18, 27	sylc 62	. . . 4 ⊢ (𝑓:𝐴–1-1-onto→{∅} → ∃𝑥 𝐴 = {𝑥})
29	28	exlimiv 1651	. . 3 ⊢ (∃𝑓 𝑓:𝐴–1-1-onto→{∅} → ∃𝑥 𝐴 = {𝑥})
30	4, 29	sylbi 121	. 2 ⊢ (𝐴 ≈ 1o → ∃𝑥 𝐴 = {𝑥})
31		vex 2824	. . . . 5 ⊢ 𝑥 ∈ V
32	31	ensn1 7087	. . . 4 ⊢ {𝑥} ≈ 1o
33		breq1 4134	. . . 4 ⊢ (𝐴 = {𝑥} → (𝐴 ≈ 1o ↔ {𝑥} ≈ 1o))
34	32, 33	mpbiri 168	. . 3 ⊢ (𝐴 = {𝑥} → 𝐴 ≈ 1o)
35	34	exlimiv 1651	. 2 ⊢ (∃𝑥 𝐴 = {𝑥} → 𝐴 ≈ 1o)
36	30, 35	impbii 126	1 ⊢ (𝐴 ≈ 1o ↔ ∃𝑥 𝐴 = {𝑥})

This proof depends on syntax axioms:   → wi 4   ↔ wb 105   = wceq 1402  ∃wex 1545   ∈ wcel 2209  Vcvv 2821  ∅c0 3520  {csn 3709  ⟨cop 3712   class class class wbr 4131  ^◡ccnv 4775  ran crn 4777   Fn wfn 5375  ⟶wf 5376  –onto→wfo 5378  –1-1-onto→wf1o 5379  ‘cfv 5380  1_oc1o 6684   ≈ cen 7024

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 623  ax-in2 624  ax-io 721  ax-5 1500  ax-7 1501  ax-gen 1502  ax-ie1 1546  ax-ie2 1547  ax-8 1557  ax-10 1558  ax-11 1559  ax-i12 1560  ax-bndl 1562  ax-4 1563  ax-17 1579  ax-i9 1583  ax-ial 1587  ax-i5r 1588  ax-14 2212  ax-ext 2220  ax-sep 4251  ax-nul 4261  ax-pow 4313  ax-pr 4348  ax-un 4580

This proof depends on definitions:  df-bi 117  df-3an 1011  df-tru 1405  df-nf 1514  df-sb 1816  df-eu 2089  df-mo 2090  df-clab 2225  df-cleq 2231  df-clel 2234  df-nfc 2381  df-ral 2533  df-rex 2534  df-reu 2535  df-v 2823  df-sbc 3052  df-dif 3222  df-un 3224  df-in 3226  df-ss 3233  df-nul 3521  df-pw 3690  df-sn 3715  df-pr 3716  df-op 3718  df-uni 3936  df-br 4132  df-opab 4194  df-id 4440  df-suc 4518  df-xp 4782  df-rel 4783  df-cnv 4784  df-co 4785  df-dm 4786  df-rn 4787  df-res 4788  df-ima 4789  df-iota 5340  df-fun 5382  df-fn 5383  df-f 5384  df-f1 5385  df-fo 5386  df-f1o 5387  df-fv 5388  df-1o 6691  df-en 7027

This theorem is used by:  en1bg  7091  reuen1  7092  eqsndc  7214  pm54.43  7542  upgrex  16549  vtxdumgrfival  16744  1loopgrvd2fi  16751