Theorem frgrncvvdeqlem2 28355

Description: Lemma 2 for frgrncvvdeq 28364. In a friendship graph, for each neighbor of a vertex there is exactly one neighbor of another vertex so that there is an edge between these two neighbors. (Contributed by Alexander van der Vekens, 22-Dec-2017.) (Revised by AV, 10-May-2021.) (Proof shortened by AV, 12-Feb-2022.)

Hypotheses

Ref	Expression
frgrncvvdeq.v1	⊢ 𝑉 = (Vtx‘𝐺)
frgrncvvdeq.e	⊢ 𝐸 = (Edg‘𝐺)
frgrncvvdeq.nx	⊢ 𝐷 = (𝐺 NeighbVtx 𝑋)
frgrncvvdeq.ny	⊢ 𝑁 = (𝐺 NeighbVtx 𝑌)
frgrncvvdeq.x	⊢ (𝜑 → 𝑋 ∈ 𝑉)
frgrncvvdeq.y	⊢ (𝜑 → 𝑌 ∈ 𝑉)
frgrncvvdeq.ne	⊢ (𝜑 → 𝑋 ≠ 𝑌)
frgrncvvdeq.xy	⊢ (𝜑 → 𝑌 ∉ 𝐷)
frgrncvvdeq.f	⊢ (𝜑 → 𝐺 ∈ FriendGraph )
frgrncvvdeq.a	⊢ 𝐴 = (𝑥 ∈ 𝐷 ↦ (℩𝑦 ∈ 𝑁 {𝑥, 𝑦} ∈ 𝐸))

Assertion

Ref	Expression
frgrncvvdeqlem2	⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → ∃!𝑦 ∈ 𝑁 {𝑥, 𝑦} ∈ 𝐸)

Distinct variable groups:   𝑦,𝐸   𝑦,𝐺   𝑦,𝑉   𝑦,𝑌   𝑥,𝑦

Allowed substitution hints:   𝜑(𝑥,𝑦)   𝐴(𝑥,𝑦)   𝐷(𝑥,𝑦)   𝐸(𝑥)   𝐺(𝑥)   𝑁(𝑥,𝑦)   𝑉(𝑥)   𝑋(𝑥,𝑦)   𝑌(𝑥)

Proof of Theorem frgrncvvdeqlem2

Step	Hyp	Ref	Expression
1		frgrncvvdeq.f	. . . 4 ⊢ (𝜑 → 𝐺 ∈ FriendGraph )
2	1	adantr 484	. . 3 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → 𝐺 ∈ FriendGraph )
3		frgrncvvdeq.nx	. . . . . . 7 ⊢ 𝐷 = (𝐺 NeighbVtx 𝑋)
4	3	eleq2i 2825	. . . . . 6 ⊢ (𝑥 ∈ 𝐷 ↔ 𝑥 ∈ (𝐺 NeighbVtx 𝑋))
5		frgrncvvdeq.v1	. . . . . . . 8 ⊢ 𝑉 = (Vtx‘𝐺)
6	5	nbgrisvtx 27401	. . . . . . 7 ⊢ (𝑥 ∈ (𝐺 NeighbVtx 𝑋) → 𝑥 ∈ 𝑉)
7	6	a1i 11	. . . . . 6 ⊢ (𝜑 → (𝑥 ∈ (𝐺 NeighbVtx 𝑋) → 𝑥 ∈ 𝑉))
8	4, 7	syl5bi 245	. . . . 5 ⊢ (𝜑 → (𝑥 ∈ 𝐷 → 𝑥 ∈ 𝑉))
9	8	imp 410	. . . 4 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → 𝑥 ∈ 𝑉)
10		frgrncvvdeq.y	. . . . 5 ⊢ (𝜑 → 𝑌 ∈ 𝑉)
11	10	adantr 484	. . . 4 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → 𝑌 ∈ 𝑉)
12		frgrncvvdeq.xy	. . . . . 6 ⊢ (𝜑 → 𝑌 ∉ 𝐷)
13		elnelne2 3050	. . . . . . 7 ⊢ ((𝑥 ∈ 𝐷 ∧ 𝑌 ∉ 𝐷) → 𝑥 ≠ 𝑌)
14	13	expcom 417	. . . . . 6 ⊢ (𝑌 ∉ 𝐷 → (𝑥 ∈ 𝐷 → 𝑥 ≠ 𝑌))
15	12, 14	syl 17	. . . . 5 ⊢ (𝜑 → (𝑥 ∈ 𝐷 → 𝑥 ≠ 𝑌))
16	15	imp 410	. . . 4 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → 𝑥 ≠ 𝑌)
17	9, 11, 16	3jca 1130	. . 3 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → (𝑥 ∈ 𝑉 ∧ 𝑌 ∈ 𝑉 ∧ 𝑥 ≠ 𝑌))
18		frgrncvvdeq.e	. . . 4 ⊢ 𝐸 = (Edg‘𝐺)
19	5, 18	frcond1 28321	. . 3 ⊢ (𝐺 ∈ FriendGraph → ((𝑥 ∈ 𝑉 ∧ 𝑌 ∈ 𝑉 ∧ 𝑥 ≠ 𝑌) → ∃!𝑦 ∈ 𝑉 {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸))
20	2, 17, 19	sylc 65	. 2 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → ∃!𝑦 ∈ 𝑉 {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸)
21		frgrusgr 28316	. . . 4 ⊢ (𝐺 ∈ FriendGraph → 𝐺 ∈ USGraph)
22		prex 5314	. . . . . . . . . . . 12 ⊢ {𝑥, 𝑦} ∈ V
23		prex 5314	. . . . . . . . . . . 12 ⊢ {𝑦, 𝑌} ∈ V
24	22, 23	prss 4723	. . . . . . . . . . 11 ⊢ (({𝑥, 𝑦} ∈ 𝐸 ∧ {𝑦, 𝑌} ∈ 𝐸) ↔ {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸)
25		ancom 464	. . . . . . . . . . 11 ⊢ (({𝑥, 𝑦} ∈ 𝐸 ∧ {𝑦, 𝑌} ∈ 𝐸) ↔ ({𝑦, 𝑌} ∈ 𝐸 ∧ {𝑥, 𝑦} ∈ 𝐸))
26	24, 25	bitr3i 280	. . . . . . . . . 10 ⊢ ({{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸 ↔ ({𝑦, 𝑌} ∈ 𝐸 ∧ {𝑥, 𝑦} ∈ 𝐸))
27	26	anbi2i 626	. . . . . . . . 9 ⊢ ((𝑦 ∈ 𝑉 ∧ {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸) ↔ (𝑦 ∈ 𝑉 ∧ ({𝑦, 𝑌} ∈ 𝐸 ∧ {𝑥, 𝑦} ∈ 𝐸)))
28		usgrumgr 27242	. . . . . . . . . . . 12 ⊢ (𝐺 ∈ USGraph → 𝐺 ∈ UMGraph)
29	5, 18	umgrpredgv 27203	. . . . . . . . . . . . . 14 ⊢ ((𝐺 ∈ UMGraph ∧ {𝑥, 𝑦} ∈ 𝐸) → (𝑥 ∈ 𝑉 ∧ 𝑦 ∈ 𝑉))
30	29	simprd 499	. . . . . . . . . . . . 13 ⊢ ((𝐺 ∈ UMGraph ∧ {𝑥, 𝑦} ∈ 𝐸) → 𝑦 ∈ 𝑉)
31	30	ex 416	. . . . . . . . . . . 12 ⊢ (𝐺 ∈ UMGraph → ({𝑥, 𝑦} ∈ 𝐸 → 𝑦 ∈ 𝑉))
32	28, 31	syl 17	. . . . . . . . . . 11 ⊢ (𝐺 ∈ USGraph → ({𝑥, 𝑦} ∈ 𝐸 → 𝑦 ∈ 𝑉))
33	32	adantld 494	. . . . . . . . . 10 ⊢ (𝐺 ∈ USGraph → (({𝑦, 𝑌} ∈ 𝐸 ∧ {𝑥, 𝑦} ∈ 𝐸) → 𝑦 ∈ 𝑉))
34	33	pm4.71rd 566	. . . . . . . . 9 ⊢ (𝐺 ∈ USGraph → (({𝑦, 𝑌} ∈ 𝐸 ∧ {𝑥, 𝑦} ∈ 𝐸) ↔ (𝑦 ∈ 𝑉 ∧ ({𝑦, 𝑌} ∈ 𝐸 ∧ {𝑥, 𝑦} ∈ 𝐸))))
35	27, 34	bitr4id 293	. . . . . . . 8 ⊢ (𝐺 ∈ USGraph → ((𝑦 ∈ 𝑉 ∧ {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸) ↔ ({𝑦, 𝑌} ∈ 𝐸 ∧ {𝑥, 𝑦} ∈ 𝐸)))
36		frgrncvvdeq.ny	. . . . . . . . . . 11 ⊢ 𝑁 = (𝐺 NeighbVtx 𝑌)
37	36	eleq2i 2825	. . . . . . . . . 10 ⊢ (𝑦 ∈ 𝑁 ↔ 𝑦 ∈ (𝐺 NeighbVtx 𝑌))
38	18	nbusgreledg 27413	. . . . . . . . . 10 ⊢ (𝐺 ∈ USGraph → (𝑦 ∈ (𝐺 NeighbVtx 𝑌) ↔ {𝑦, 𝑌} ∈ 𝐸))
39	37, 38	bitr2id 287	. . . . . . . . 9 ⊢ (𝐺 ∈ USGraph → ({𝑦, 𝑌} ∈ 𝐸 ↔ 𝑦 ∈ 𝑁))
40	39	anbi1d 633	. . . . . . . 8 ⊢ (𝐺 ∈ USGraph → (({𝑦, 𝑌} ∈ 𝐸 ∧ {𝑥, 𝑦} ∈ 𝐸) ↔ (𝑦 ∈ 𝑁 ∧ {𝑥, 𝑦} ∈ 𝐸)))
41	35, 40	bitrd 282	. . . . . . 7 ⊢ (𝐺 ∈ USGraph → ((𝑦 ∈ 𝑉 ∧ {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸) ↔ (𝑦 ∈ 𝑁 ∧ {𝑥, 𝑦} ∈ 𝐸)))
42	41	eubidv 2583	. . . . . 6 ⊢ (𝐺 ∈ USGraph → (∃!𝑦(𝑦 ∈ 𝑉 ∧ {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸) ↔ ∃!𝑦(𝑦 ∈ 𝑁 ∧ {𝑥, 𝑦} ∈ 𝐸)))
43	42	biimpd 232	. . . . 5 ⊢ (𝐺 ∈ USGraph → (∃!𝑦(𝑦 ∈ 𝑉 ∧ {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸) → ∃!𝑦(𝑦 ∈ 𝑁 ∧ {𝑥, 𝑦} ∈ 𝐸)))
44		df-reu 3061	. . . . 5 ⊢ (∃!𝑦 ∈ 𝑉 {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸 ↔ ∃!𝑦(𝑦 ∈ 𝑉 ∧ {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸))
45		df-reu 3061	. . . . 5 ⊢ (∃!𝑦 ∈ 𝑁 {𝑥, 𝑦} ∈ 𝐸 ↔ ∃!𝑦(𝑦 ∈ 𝑁 ∧ {𝑥, 𝑦} ∈ 𝐸))
46	43, 44, 45	3imtr4g 299	. . . 4 ⊢ (𝐺 ∈ USGraph → (∃!𝑦 ∈ 𝑉 {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸 → ∃!𝑦 ∈ 𝑁 {𝑥, 𝑦} ∈ 𝐸))
47	1, 21, 46	3syl 18	. . 3 ⊢ (𝜑 → (∃!𝑦 ∈ 𝑉 {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸 → ∃!𝑦 ∈ 𝑁 {𝑥, 𝑦} ∈ 𝐸))
48	47	adantr 484	. 2 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → (∃!𝑦 ∈ 𝑉 {{𝑥, 𝑦}, {𝑦, 𝑌}} ⊆ 𝐸 → ∃!𝑦 ∈ 𝑁 {𝑥, 𝑦} ∈ 𝐸))
49	20, 48	mpd 15	1 ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐷) → ∃!𝑦 ∈ 𝑁 {𝑥, 𝑦} ∈ 𝐸)

Syntax hints:   → wi 4   ∧ wa 399   ∧ w3a 1089   = wceq 1543   ∈ wcel 2110  ∃!weu 2565   ≠ wne 2935   ∉ wnel 3039  ∃!wreu 3056   ⊆ wss 3857  {cpr 4533   ↦ cmpt 5124  ‘cfv 6369  ℩crio 7158  (class class class)co 7202  Vtxcvtx 27059  Edgcedg 27110  UMGraphcumgr 27144  USGraphcusgr 27212   NeighbVtx cnbgr 27392   FriendGraph cfrgr 28313

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1803  ax-4 1817  ax-5 1918  ax-6 1976  ax-7 2016  ax-8 2112  ax-9 2120  ax-10 2141  ax-11 2158  ax-12 2175  ax-ext 2706  ax-sep 5181  ax-nul 5188  ax-pow 5247  ax-pr 5311  ax-un 7512  ax-cnex 10768  ax-resscn 10769  ax-1cn 10770  ax-icn 10771  ax-addcl 10772  ax-addrcl 10773  ax-mulcl 10774  ax-mulrcl 10775  ax-mulcom 10776  ax-addass 10777  ax-mulass 10778  ax-distr 10779  ax-i2m1 10780  ax-1ne0 10781  ax-1rid 10782  ax-rnegex 10783  ax-rrecex 10784  ax-cnre 10785  ax-pre-lttri 10786  ax-pre-lttrn 10787  ax-pre-ltadd 10788  ax-pre-mulgt0 10789

This theorem depends on definitions:  df-bi 210  df-an 400  df-or 848  df-3or 1090  df-3an 1091  df-tru 1546  df-fal 1556  df-ex 1788  df-nf 1792  df-sb 2071  df-mo 2537  df-eu 2566  df-clab 2713  df-cleq 2726  df-clel 2812  df-nfc 2882  df-ne 2936  df-nel 3040  df-ral 3059  df-rex 3060  df-reu 3061  df-rab 3063  df-v 3403  df-sbc 3688  df-csb 3803  df-dif 3860  df-un 3862  df-in 3864  df-ss 3874  df-pss 3876  df-nul 4228  df-if 4430  df-pw 4505  df-sn 4532  df-pr 4534  df-tp 4536  df-op 4538  df-uni 4810  df-int 4850  df-iun 4896  df-br 5044  df-opab 5106  df-mpt 5125  df-tr 5151  df-id 5444  df-eprel 5449  df-po 5457  df-so 5458  df-fr 5498  df-we 5500  df-xp 5546  df-rel 5547  df-cnv 5548  df-co 5549  df-dm 5550  df-rn 5551  df-res 5552  df-ima 5553  df-pred 6149  df-ord 6205  df-on 6206  df-lim 6207  df-suc 6208  df-iota 6327  df-fun 6371  df-fn 6372  df-f 6373  df-f1 6374  df-fo 6375  df-f1o 6376  df-fv 6377  df-riota 7159  df-ov 7205  df-oprab 7206  df-mpo 7207  df-om 7634  df-1st 7750  df-2nd 7751  df-wrecs 8036  df-recs 8097  df-rdg 8135  df-1o 8191  df-2o 8192  df-oadd 8195  df-er 8380  df-en 8616  df-dom 8617  df-sdom 8618  df-fin 8619  df-dju 9500  df-card 9538  df-pnf 10852  df-mnf 10853  df-xr 10854  df-ltxr 10855  df-le 10856  df-sub 11047  df-neg 11048  df-nn 11814  df-2 11876  df-n0 12074  df-xnn0 12146  df-z 12160  df-uz 12422  df-fz 13079  df-hash 13880  df-edg 27111  df-upgr 27145  df-umgr 27146  df-usgr 27214  df-nbgr 27393  df-frgr 28314

This theorem is referenced by:  frgrncvvdeqlem3  28356  frgrncvvdeqlem4  28357