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Theorem uvtx01vtx 27112
 Description: If a graph/class has no edges, it has universal vertices if and only if it has exactly one vertex. (Contributed by Alexander van der Vekens, 12-Oct-2017.) (Revised by AV, 30-Oct-2020.) (Revised by AV, 14-Feb-2022.)
Hypotheses
Ref Expression
uvtxel.v 𝑉 = (Vtx‘𝐺)
isuvtx.e 𝐸 = (Edg‘𝐺)
Assertion
Ref Expression
uvtx01vtx (𝐸 = ∅ → ((UnivVtx‘𝐺) ≠ ∅ ↔ (♯‘𝑉) = 1))

Proof of Theorem uvtx01vtx
Dummy variables 𝑛 𝑣 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 uvtxel.v . . . . 5 𝑉 = (Vtx‘𝐺)
21uvtxval 27102 . . . 4 (UnivVtx‘𝐺) = {𝑣𝑉 ∣ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣)}
32a1i 11 . . 3 (𝐸 = ∅ → (UnivVtx‘𝐺) = {𝑣𝑉 ∣ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣)})
43neeq1d 3080 . 2 (𝐸 = ∅ → ((UnivVtx‘𝐺) ≠ ∅ ↔ {𝑣𝑉 ∣ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣)} ≠ ∅))
5 rabn0 4343 . . 3 ({𝑣𝑉 ∣ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣)} ≠ ∅ ↔ ∃𝑣𝑉𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣))
65a1i 11 . 2 (𝐸 = ∅ → ({𝑣𝑉 ∣ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣)} ≠ ∅ ↔ ∃𝑣𝑉𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣)))
7 falseral0 4462 . . . . . . . . . 10 ((∀𝑛 ¬ 𝑛 ∈ ∅ ∧ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅) → (𝑉 ∖ {𝑣}) = ∅)
87ex 413 . . . . . . . . 9 (∀𝑛 ¬ 𝑛 ∈ ∅ → (∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅ → (𝑉 ∖ {𝑣}) = ∅))
9 noel 4300 . . . . . . . . 9 ¬ 𝑛 ∈ ∅
108, 9mpg 1791 . . . . . . . 8 (∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅ → (𝑉 ∖ {𝑣}) = ∅)
11 ssdif0 4327 . . . . . . . . 9 (𝑉 ⊆ {𝑣} ↔ (𝑉 ∖ {𝑣}) = ∅)
12 sssn 4758 . . . . . . . . . 10 (𝑉 ⊆ {𝑣} ↔ (𝑉 = ∅ ∨ 𝑉 = {𝑣}))
13 ne0i 4304 . . . . . . . . . . . 12 (𝑣𝑉𝑉 ≠ ∅)
14 eqneqall 3032 . . . . . . . . . . . 12 (𝑉 = ∅ → (𝑉 ≠ ∅ → 𝑉 = {𝑣}))
1513, 14syl5 34 . . . . . . . . . . 11 (𝑉 = ∅ → (𝑣𝑉𝑉 = {𝑣}))
16 ax-1 6 . . . . . . . . . . 11 (𝑉 = {𝑣} → (𝑣𝑉𝑉 = {𝑣}))
1715, 16jaoi 853 . . . . . . . . . 10 ((𝑉 = ∅ ∨ 𝑉 = {𝑣}) → (𝑣𝑉𝑉 = {𝑣}))
1812, 17sylbi 218 . . . . . . . . 9 (𝑉 ⊆ {𝑣} → (𝑣𝑉𝑉 = {𝑣}))
1911, 18sylbir 236 . . . . . . . 8 ((𝑉 ∖ {𝑣}) = ∅ → (𝑣𝑉𝑉 = {𝑣}))
2010, 19syl 17 . . . . . . 7 (∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅ → (𝑣𝑉𝑉 = {𝑣}))
2120impcom 408 . . . . . 6 ((𝑣𝑉 ∧ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅) → 𝑉 = {𝑣})
22 vsnid 4599 . . . . . . . 8 𝑣 ∈ {𝑣}
23 eleq2 2906 . . . . . . . 8 (𝑉 = {𝑣} → (𝑣𝑉𝑣 ∈ {𝑣}))
2422, 23mpbiri 259 . . . . . . 7 (𝑉 = {𝑣} → 𝑣𝑉)
25 ralel 3154 . . . . . . . 8 𝑛 ∈ ∅ 𝑛 ∈ ∅
26 difeq1 4096 . . . . . . . . . 10 (𝑉 = {𝑣} → (𝑉 ∖ {𝑣}) = ({𝑣} ∖ {𝑣}))
27 difid 4334 . . . . . . . . . 10 ({𝑣} ∖ {𝑣}) = ∅
2826, 27syl6eq 2877 . . . . . . . . 9 (𝑉 = {𝑣} → (𝑉 ∖ {𝑣}) = ∅)
2928raleqdv 3421 . . . . . . . 8 (𝑉 = {𝑣} → (∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅ ↔ ∀𝑛 ∈ ∅ 𝑛 ∈ ∅))
3025, 29mpbiri 259 . . . . . . 7 (𝑉 = {𝑣} → ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅)
3124, 30jca 512 . . . . . 6 (𝑉 = {𝑣} → (𝑣𝑉 ∧ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅))
3221, 31impbii 210 . . . . 5 ((𝑣𝑉 ∧ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅) ↔ 𝑉 = {𝑣})
3332a1i 11 . . . 4 (𝐸 = ∅ → ((𝑣𝑉 ∧ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅) ↔ 𝑉 = {𝑣}))
3433exbidv 1915 . . 3 (𝐸 = ∅ → (∃𝑣(𝑣𝑉 ∧ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅) ↔ ∃𝑣 𝑉 = {𝑣}))
35 isuvtx.e . . . . . . . 8 𝐸 = (Edg‘𝐺)
3635eqeq1i 2831 . . . . . . 7 (𝐸 = ∅ ↔ (Edg‘𝐺) = ∅)
37 nbgr0edg 27072 . . . . . . 7 ((Edg‘𝐺) = ∅ → (𝐺 NeighbVtx 𝑣) = ∅)
3836, 37sylbi 218 . . . . . 6 (𝐸 = ∅ → (𝐺 NeighbVtx 𝑣) = ∅)
3938eleq2d 2903 . . . . 5 (𝐸 = ∅ → (𝑛 ∈ (𝐺 NeighbVtx 𝑣) ↔ 𝑛 ∈ ∅))
4039rexralbidv 3306 . . . 4 (𝐸 = ∅ → (∃𝑣𝑉𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣) ↔ ∃𝑣𝑉𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅))
41 df-rex 3149 . . . 4 (∃𝑣𝑉𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅ ↔ ∃𝑣(𝑣𝑉 ∧ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅))
4240, 41syl6bb 288 . . 3 (𝐸 = ∅ → (∃𝑣𝑉𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣) ↔ ∃𝑣(𝑣𝑉 ∧ ∀𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ ∅)))
431fvexi 6683 . . . 4 𝑉 ∈ V
44 hash1snb 13775 . . . 4 (𝑉 ∈ V → ((♯‘𝑉) = 1 ↔ ∃𝑣 𝑉 = {𝑣}))
4543, 44mp1i 13 . . 3 (𝐸 = ∅ → ((♯‘𝑉) = 1 ↔ ∃𝑣 𝑉 = {𝑣}))
4634, 42, 453bitr4d 312 . 2 (𝐸 = ∅ → (∃𝑣𝑉𝑛 ∈ (𝑉 ∖ {𝑣})𝑛 ∈ (𝐺 NeighbVtx 𝑣) ↔ (♯‘𝑉) = 1))
474, 6, 463bitrd 306 1 (𝐸 = ∅ → ((UnivVtx‘𝐺) ≠ ∅ ↔ (♯‘𝑉) = 1))
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 207   ∧ wa 396   ∨ wo 843  ∀wal 1528   = wceq 1530  ∃wex 1773   ∈ wcel 2107   ≠ wne 3021  ∀wral 3143  ∃wrex 3144  {crab 3147  Vcvv 3500   ∖ cdif 3937   ⊆ wss 3940  ∅c0 4295  {csn 4564  ‘cfv 6354  (class class class)co 7150  1c1 10532  ♯chash 13685  Vtxcvtx 26714  Edgcedg 26765   NeighbVtx cnbgr 27047  UnivVtxcuvtx 27100 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1789  ax-4 1803  ax-5 1904  ax-6 1963  ax-7 2008  ax-8 2109  ax-9 2117  ax-10 2138  ax-11 2153  ax-12 2169  ax-ext 2798  ax-rep 5187  ax-sep 5200  ax-nul 5207  ax-pow 5263  ax-pr 5326  ax-un 7455  ax-cnex 10587  ax-resscn 10588  ax-1cn 10589  ax-icn 10590  ax-addcl 10591  ax-addrcl 10592  ax-mulcl 10593  ax-mulrcl 10594  ax-mulcom 10595  ax-addass 10596  ax-mulass 10597  ax-distr 10598  ax-i2m1 10599  ax-1ne0 10600  ax-1rid 10601  ax-rnegex 10602  ax-rrecex 10603  ax-cnre 10604  ax-pre-lttri 10605  ax-pre-lttrn 10606  ax-pre-ltadd 10607  ax-pre-mulgt0 10608 This theorem depends on definitions:  df-bi 208  df-an 397  df-or 844  df-3or 1082  df-3an 1083  df-tru 1533  df-fal 1543  df-ex 1774  df-nf 1778  df-sb 2063  df-mo 2620  df-eu 2652  df-clab 2805  df-cleq 2819  df-clel 2898  df-nfc 2968  df-ne 3022  df-nel 3129  df-ral 3148  df-rex 3149  df-reu 3150  df-rmo 3151  df-rab 3152  df-v 3502  df-sbc 3777  df-csb 3888  df-dif 3943  df-un 3945  df-in 3947  df-ss 3956  df-pss 3958  df-nul 4296  df-if 4471  df-pw 4544  df-sn 4565  df-pr 4567  df-tp 4569  df-op 4571  df-uni 4838  df-int 4875  df-iun 4919  df-br 5064  df-opab 5126  df-mpt 5144  df-tr 5170  df-id 5459  df-eprel 5464  df-po 5473  df-so 5474  df-fr 5513  df-we 5515  df-xp 5560  df-rel 5561  df-cnv 5562  df-co 5563  df-dm 5564  df-rn 5565  df-res 5566  df-ima 5567  df-pred 6147  df-ord 6193  df-on 6194  df-lim 6195  df-suc 6196  df-iota 6313  df-fun 6356  df-fn 6357  df-f 6358  df-f1 6359  df-fo 6360  df-f1o 6361  df-fv 6362  df-riota 7108  df-ov 7153  df-oprab 7154  df-mpo 7155  df-om 7574  df-1st 7685  df-2nd 7686  df-wrecs 7943  df-recs 8004  df-rdg 8042  df-1o 8098  df-oadd 8102  df-er 8284  df-en 8504  df-dom 8505  df-sdom 8506  df-fin 8507  df-dju 9324  df-card 9362  df-pnf 10671  df-mnf 10672  df-xr 10673  df-ltxr 10674  df-le 10675  df-sub 10866  df-neg 10867  df-nn 11633  df-n0 11892  df-z 11976  df-uz 12238  df-fz 12888  df-hash 13686  df-nbgr 27048  df-uvtx 27101 This theorem is referenced by: (None)
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