Theorem snnen2o 8691

Description: A singleton {𝐴} is never equinumerous with the ordinal number 2. This holds for proper singletons (𝐴 ∈ V) as well as for singletons being the empty set (𝐴 ∉ V). (Contributed by AV, 6-Aug-2019.)

Assertion

Ref	Expression
snnen2o	⊢ ¬ {𝐴} ≈ 2o

Proof of Theorem snnen2o

Step	Hyp	Ref	Expression
1		1onn 8248	. . . 4 ⊢ 1o ∈ ω
2		php5 8689	. . . 4 ⊢ (1o ∈ ω → ¬ 1o ≈ suc 1o)
3	1, 2	ax-mp 5	. . 3 ⊢ ¬ 1o ≈ suc 1o
4		ensn1g 8557	. . 3 ⊢ (𝐴 ∈ V → {𝐴} ≈ 1o)
5		df-2o 8086	. . . . . 6 ⊢ 2o = suc 1o
6	5	eqcomi 2807	. . . . 5 ⊢ suc 1o = 2o
7	6	breq2i 5038	. . . 4 ⊢ (1o ≈ suc 1o ↔ 1o ≈ 2o)
8		ensymb 8540	. . . . . 6 ⊢ ({𝐴} ≈ 1o ↔ 1o ≈ {𝐴})
9		entr 8544	. . . . . . 7 ⊢ ((1o ≈ {𝐴} ∧ {𝐴} ≈ 2o) → 1o ≈ 2o)
10	9	ex 416	. . . . . 6 ⊢ (1o ≈ {𝐴} → ({𝐴} ≈ 2o → 1o ≈ 2o))
11	8, 10	sylbi 220	. . . . 5 ⊢ ({𝐴} ≈ 1o → ({𝐴} ≈ 2o → 1o ≈ 2o))
12	11	con3rr3 158	. . . 4 ⊢ (¬ 1o ≈ 2o → ({𝐴} ≈ 1o → ¬ {𝐴} ≈ 2o))
13	7, 12	sylnbi 333	. . 3 ⊢ (¬ 1o ≈ suc 1o → ({𝐴} ≈ 1o → ¬ {𝐴} ≈ 2o))
14	3, 4, 13	mpsyl 68	. 2 ⊢ (𝐴 ∈ V → ¬ {𝐴} ≈ 2o)
15		2on0 8096	. . . 4 ⊢ 2o ≠ ∅
16		ensymb 8540	. . . . 5 ⊢ (∅ ≈ 2o ↔ 2o ≈ ∅)
17		en0 8555	. . . . 5 ⊢ (2o ≈ ∅ ↔ 2o = ∅)
18	16, 17	bitri 278	. . . 4 ⊢ (∅ ≈ 2o ↔ 2o = ∅)
19	15, 18	nemtbir 3082	. . 3 ⊢ ¬ ∅ ≈ 2o
20		snprc 4613	. . . . 5 ⊢ (¬ 𝐴 ∈ V ↔ {𝐴} = ∅)
21	20	biimpi 219	. . . 4 ⊢ (¬ 𝐴 ∈ V → {𝐴} = ∅)
22	21	breq1d 5040	. . 3 ⊢ (¬ 𝐴 ∈ V → ({𝐴} ≈ 2o ↔ ∅ ≈ 2o))
23	19, 22	mtbiri 330	. 2 ⊢ (¬ 𝐴 ∈ V → ¬ {𝐴} ≈ 2o)
24	14, 23	pm2.61i 185	1 ⊢ ¬ {𝐴} ≈ 2o

Syntax hints:  ¬ wn 3   → wi 4   = wceq 1538   ∈ wcel 2111  Vcvv 3441  ∅c0 4243  {csn 4525   class class class wbr 5030  suc csuc 6161  ωcom 7560  1_oc1o 8078  2_oc2o 8079   ≈ cen 8489

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 1911  ax-6 1970  ax-7 2015  ax-8 2113  ax-9 2121  ax-10 2142  ax-11 2158  ax-12 2175  ax-ext 2770  ax-sep 5167  ax-nul 5174  ax-pow 5231  ax-pr 5295  ax-un 7441

This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-3or 1085  df-3an 1086  df-tru 1541  df-ex 1782  df-nf 1786  df-sb 2070  df-mo 2598  df-eu 2629  df-clab 2777  df-cleq 2791  df-clel 2870  df-nfc 2938  df-ne 2988  df-ral 3111  df-rex 3112  df-rab 3115  df-v 3443  df-sbc 3721  df-dif 3884  df-un 3886  df-in 3888  df-ss 3898  df-pss 3900  df-nul 4244  df-if 4426  df-pw 4499  df-sn 4526  df-pr 4528  df-tp 4530  df-op 4532  df-uni 4801  df-br 5031  df-opab 5093  df-tr 5137  df-id 5425  df-eprel 5430  df-po 5438  df-so 5439  df-fr 5478  df-we 5480  df-xp 5525  df-rel 5526  df-cnv 5527  df-co 5528  df-dm 5529  df-rn 5530  df-res 5531  df-ima 5532  df-ord 6162  df-on 6163  df-lim 6164  df-suc 6165  df-iota 6283  df-fun 6326  df-fn 6327  df-f 6328  df-f1 6329  df-fo 6330  df-f1o 6331  df-fv 6332  df-om 7561  df-1o 8085  df-2o 8086  df-er 8272  df-en 8493  df-dom 8494  df-sdom 8495

This theorem is referenced by:  pmtrsn  18639  trivnsimpgd  19212