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Mirrors > Home > MPE Home > Th. List > vdgfrgrgt2 | Structured version Visualization version GIF version |
Description: Any vertex in a friendship graph (with more than one vertex - then, actually, the graph must have at least three vertices, because otherwise, it would not be a friendship graph) has at least degree 2, see remark 3 in [MertziosUnger] p. 153 (after Proposition 1): "It follows that deg(v) >= 2 for every node v of a friendship graph". (Contributed by Alexander van der Vekens, 21-Dec-2017.) (Revised by AV, 5-Apr-2021.) |
Ref | Expression |
---|---|
vdn1frgrv2.v | ⊢ 𝑉 = (Vtx‘𝐺) |
Ref | Expression |
---|---|
vdgfrgrgt2 | ⊢ ((𝐺 ∈ FriendGraph ∧ 𝑁 ∈ 𝑉) → (1 < (♯‘𝑉) → 2 ≤ ((VtxDeg‘𝐺)‘𝑁))) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | vdn1frgrv2.v | . . . . 5 ⊢ 𝑉 = (Vtx‘𝐺) | |
2 | 1 | vdgn0frgrv2 28350 | . . . 4 ⊢ ((𝐺 ∈ FriendGraph ∧ 𝑁 ∈ 𝑉) → (1 < (♯‘𝑉) → ((VtxDeg‘𝐺)‘𝑁) ≠ 0)) |
3 | 2 | imp 410 | . . 3 ⊢ (((𝐺 ∈ FriendGraph ∧ 𝑁 ∈ 𝑉) ∧ 1 < (♯‘𝑉)) → ((VtxDeg‘𝐺)‘𝑁) ≠ 0) |
4 | 1 | vdgn1frgrv2 28351 | . . . 4 ⊢ ((𝐺 ∈ FriendGraph ∧ 𝑁 ∈ 𝑉) → (1 < (♯‘𝑉) → ((VtxDeg‘𝐺)‘𝑁) ≠ 1)) |
5 | 4 | imp 410 | . . 3 ⊢ (((𝐺 ∈ FriendGraph ∧ 𝑁 ∈ 𝑉) ∧ 1 < (♯‘𝑉)) → ((VtxDeg‘𝐺)‘𝑁) ≠ 1) |
6 | 1 | vtxdgelxnn0 27532 | . . . . 5 ⊢ (𝑁 ∈ 𝑉 → ((VtxDeg‘𝐺)‘𝑁) ∈ ℕ0*) |
7 | xnn0n0n1ge2b 12706 | . . . . 5 ⊢ (((VtxDeg‘𝐺)‘𝑁) ∈ ℕ0* → ((((VtxDeg‘𝐺)‘𝑁) ≠ 0 ∧ ((VtxDeg‘𝐺)‘𝑁) ≠ 1) ↔ 2 ≤ ((VtxDeg‘𝐺)‘𝑁))) | |
8 | 6, 7 | syl 17 | . . . 4 ⊢ (𝑁 ∈ 𝑉 → ((((VtxDeg‘𝐺)‘𝑁) ≠ 0 ∧ ((VtxDeg‘𝐺)‘𝑁) ≠ 1) ↔ 2 ≤ ((VtxDeg‘𝐺)‘𝑁))) |
9 | 8 | ad2antlr 727 | . . 3 ⊢ (((𝐺 ∈ FriendGraph ∧ 𝑁 ∈ 𝑉) ∧ 1 < (♯‘𝑉)) → ((((VtxDeg‘𝐺)‘𝑁) ≠ 0 ∧ ((VtxDeg‘𝐺)‘𝑁) ≠ 1) ↔ 2 ≤ ((VtxDeg‘𝐺)‘𝑁))) |
10 | 3, 5, 9 | mpbi2and 712 | . 2 ⊢ (((𝐺 ∈ FriendGraph ∧ 𝑁 ∈ 𝑉) ∧ 1 < (♯‘𝑉)) → 2 ≤ ((VtxDeg‘𝐺)‘𝑁)) |
11 | 10 | ex 416 | 1 ⊢ ((𝐺 ∈ FriendGraph ∧ 𝑁 ∈ 𝑉) → (1 < (♯‘𝑉) → 2 ≤ ((VtxDeg‘𝐺)‘𝑁))) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ↔ wb 209 ∧ wa 399 = wceq 1543 ∈ wcel 2110 ≠ wne 2935 class class class wbr 5043 ‘cfv 6369 0cc0 10712 1c1 10713 < clt 10850 ≤ cle 10851 2c2 11868 ℕ0*cxnn0 12145 ♯chash 13879 Vtxcvtx 27059 VtxDegcvtxdg 27525 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-rep 5168 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-ifp 1064 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-rmo 3062 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-oadd 8195 df-er 8380 df-map 8499 df-pm 8500 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-3 11877 df-n0 12074 df-xnn0 12146 df-z 12160 df-uz 12422 df-xadd 12688 df-fz 13079 df-fzo 13222 df-hash 13880 df-word 14053 df-concat 14109 df-s1 14136 df-s2 14396 df-s3 14397 df-edg 27111 df-uhgr 27121 df-upgr 27145 df-umgr 27146 df-uspgr 27213 df-usgr 27214 df-vtxdg 27526 df-wlks 27659 df-wlkson 27660 df-trls 27752 df-trlson 27753 df-pths 27775 df-spths 27776 df-pthson 27777 df-spthson 27778 df-conngr 28242 df-frgr 28314 |
This theorem is referenced by: frgrwopreglem2 28368 |
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