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Mirrors > Home > MPE Home > Th. List > frgrregorufrg | Structured version Visualization version GIF version |
Description: If there is a vertex having degree π for each nonnegative integer π in a friendship graph, then there is a universal friend. This corresponds to claim 2 in [Huneke] p. 2: "Suppose there is a vertex of degree k > 1. ... all vertices have degree k, unless there is a universal friend. ... It follows that G is k-regular, i.e., the degree of every vertex is k". Variant of frgrregorufr 30174 with generalization. (Contributed by Alexander van der Vekens, 6-Sep-2018.) (Revised by AV, 26-May-2021.) (Proof shortened by AV, 12-Jan-2022.) |
Ref | Expression |
---|---|
frgrregorufrg.v | β’ π = (VtxβπΊ) |
frgrregorufrg.e | β’ πΈ = (EdgβπΊ) |
Ref | Expression |
---|---|
frgrregorufrg | β’ (πΊ β FriendGraph β βπ β β0 (βπ β π ((VtxDegβπΊ)βπ) = π β (πΊ RegUSGraph π β¨ βπ£ β π βπ€ β (π β {π£}){π£, π€} β πΈ))) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | frgrregorufrg.v | . . . . 5 β’ π = (VtxβπΊ) | |
2 | frgrregorufrg.e | . . . . 5 β’ πΈ = (EdgβπΊ) | |
3 | eqid 2725 | . . . . 5 β’ (VtxDegβπΊ) = (VtxDegβπΊ) | |
4 | 1, 2, 3 | frgrregorufr 30174 | . . . 4 β’ (πΊ β FriendGraph β (βπ β π ((VtxDegβπΊ)βπ) = π β (βπ£ β π ((VtxDegβπΊ)βπ£) = π β¨ βπ£ β π βπ€ β (π β {π£}){π£, π€} β πΈ))) |
5 | 4 | adantr 479 | . . 3 β’ ((πΊ β FriendGraph β§ π β β0) β (βπ β π ((VtxDegβπΊ)βπ) = π β (βπ£ β π ((VtxDegβπΊ)βπ£) = π β¨ βπ£ β π βπ€ β (π β {π£}){π£, π€} β πΈ))) |
6 | frgrusgr 30110 | . . . . 5 β’ (πΊ β FriendGraph β πΊ β USGraph) | |
7 | nn0xnn0 12573 | . . . . 5 β’ (π β β0 β π β β0*) | |
8 | 1, 3 | usgreqdrusgr 29421 | . . . . . 6 β’ ((πΊ β USGraph β§ π β β0* β§ βπ£ β π ((VtxDegβπΊ)βπ£) = π) β πΊ RegUSGraph π) |
9 | 8 | 3expia 1118 | . . . . 5 β’ ((πΊ β USGraph β§ π β β0*) β (βπ£ β π ((VtxDegβπΊ)βπ£) = π β πΊ RegUSGraph π)) |
10 | 6, 7, 9 | syl2an 594 | . . . 4 β’ ((πΊ β FriendGraph β§ π β β0) β (βπ£ β π ((VtxDegβπΊ)βπ£) = π β πΊ RegUSGraph π)) |
11 | 10 | orim1d 963 | . . 3 β’ ((πΊ β FriendGraph β§ π β β0) β ((βπ£ β π ((VtxDegβπΊ)βπ£) = π β¨ βπ£ β π βπ€ β (π β {π£}){π£, π€} β πΈ) β (πΊ RegUSGraph π β¨ βπ£ β π βπ€ β (π β {π£}){π£, π€} β πΈ))) |
12 | 5, 11 | syld 47 | . 2 β’ ((πΊ β FriendGraph β§ π β β0) β (βπ β π ((VtxDegβπΊ)βπ) = π β (πΊ RegUSGraph π β¨ βπ£ β π βπ€ β (π β {π£}){π£, π€} β πΈ))) |
13 | 12 | ralrimiva 3136 | 1 β’ (πΊ β FriendGraph β βπ β β0 (βπ β π ((VtxDegβπΊ)βπ) = π β (πΊ RegUSGraph π β¨ βπ£ β π βπ€ β (π β {π£}){π£, π€} β πΈ))) |
Colors of variables: wff setvar class |
Syntax hints: β wi 4 β§ wa 394 β¨ wo 845 = wceq 1533 β wcel 2098 βwral 3051 βwrex 3060 β cdif 3938 {csn 4625 {cpr 4627 class class class wbr 5144 βcfv 6543 β0cn0 12497 β0*cxnn0 12569 Vtxcvtx 28848 Edgcedg 28899 USGraphcusgr 29001 VtxDegcvtxdg 29318 RegUSGraph crusgr 29409 FriendGraph cfrgr 30107 |
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 1905 ax-6 1963 ax-7 2003 ax-8 2100 ax-9 2108 ax-10 2129 ax-11 2146 ax-12 2166 ax-ext 2696 ax-rep 5281 ax-sep 5295 ax-nul 5302 ax-pow 5360 ax-pr 5424 ax-un 7735 ax-cnex 11189 ax-resscn 11190 ax-1cn 11191 ax-icn 11192 ax-addcl 11193 ax-addrcl 11194 ax-mulcl 11195 ax-mulrcl 11196 ax-mulcom 11197 ax-addass 11198 ax-mulass 11199 ax-distr 11200 ax-i2m1 11201 ax-1ne0 11202 ax-1rid 11203 ax-rnegex 11204 ax-rrecex 11205 ax-cnre 11206 ax-pre-lttri 11207 ax-pre-lttrn 11208 ax-pre-ltadd 11209 ax-pre-mulgt0 11210 |
This theorem depends on definitions: df-bi 206 df-an 395 df-or 846 df-3or 1085 df-3an 1086 df-tru 1536 df-fal 1546 df-ex 1774 df-nf 1778 df-sb 2060 df-mo 2528 df-eu 2557 df-clab 2703 df-cleq 2717 df-clel 2802 df-nfc 2877 df-ne 2931 df-nel 3037 df-ral 3052 df-rex 3061 df-rmo 3364 df-reu 3365 df-rab 3420 df-v 3465 df-sbc 3771 df-csb 3887 df-dif 3944 df-un 3946 df-in 3948 df-ss 3958 df-pss 3961 df-nul 4320 df-if 4526 df-pw 4601 df-sn 4626 df-pr 4628 df-op 4632 df-uni 4905 df-int 4946 df-iun 4994 df-br 5145 df-opab 5207 df-mpt 5228 df-tr 5262 df-id 5571 df-eprel 5577 df-po 5585 df-so 5586 df-fr 5628 df-we 5630 df-xp 5679 df-rel 5680 df-cnv 5681 df-co 5682 df-dm 5683 df-rn 5684 df-res 5685 df-ima 5686 df-pred 6301 df-ord 6368 df-on 6369 df-lim 6370 df-suc 6371 df-iota 6495 df-fun 6545 df-fn 6546 df-f 6547 df-f1 6548 df-fo 6549 df-f1o 6550 df-fv 6551 df-riota 7369 df-ov 7416 df-oprab 7417 df-mpo 7418 df-om 7866 df-1st 7987 df-2nd 7988 df-frecs 8280 df-wrecs 8311 df-recs 8385 df-rdg 8424 df-1o 8480 df-2o 8481 df-oadd 8484 df-er 8718 df-en 8958 df-dom 8959 df-sdom 8960 df-fin 8961 df-dju 9919 df-card 9957 df-pnf 11275 df-mnf 11276 df-xr 11277 df-ltxr 11278 df-le 11279 df-sub 11471 df-neg 11472 df-nn 12238 df-2 12300 df-n0 12498 df-xnn0 12570 df-z 12584 df-uz 12848 df-xadd 13120 df-fz 13512 df-hash 14317 df-edg 28900 df-uhgr 28910 df-ushgr 28911 df-upgr 28934 df-umgr 28935 df-uspgr 29002 df-usgr 29003 df-nbgr 29185 df-vtxdg 29319 df-rgr 29410 df-rusgr 29411 df-frgr 30108 |
This theorem is referenced by: friendshipgt3 30247 |
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