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Mirrors > Home > MPE Home > Th. List > frgrwopreglem2 | Structured version Visualization version GIF version |
Description: Lemma 2 for frgrwopreg 28101. If the set 𝐴 of vertices of degree 𝐾 is not empty in a friendship graph with at least two vertices, then 𝐾 must be greater than 1 . This is only an observation, which is not required for the proof the friendship theorem. (Contributed by Alexander van der Vekens, 30-Dec-2017.) (Revised by AV, 2-Jan-2022.) |
Ref | Expression |
---|---|
frgrwopreg.v | ⊢ 𝑉 = (Vtx‘𝐺) |
frgrwopreg.d | ⊢ 𝐷 = (VtxDeg‘𝐺) |
frgrwopreg.a | ⊢ 𝐴 = {𝑥 ∈ 𝑉 ∣ (𝐷‘𝑥) = 𝐾} |
frgrwopreg.b | ⊢ 𝐵 = (𝑉 ∖ 𝐴) |
Ref | Expression |
---|---|
frgrwopreglem2 | ⊢ ((𝐺 ∈ FriendGraph ∧ 1 < (♯‘𝑉) ∧ 𝐴 ≠ ∅) → 2 ≤ 𝐾) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | n0 4309 | . . 3 ⊢ (𝐴 ≠ ∅ ↔ ∃𝑥 𝑥 ∈ 𝐴) | |
2 | frgrwopreg.a | . . . . . 6 ⊢ 𝐴 = {𝑥 ∈ 𝑉 ∣ (𝐷‘𝑥) = 𝐾} | |
3 | 2 | rabeq2i 3487 | . . . . 5 ⊢ (𝑥 ∈ 𝐴 ↔ (𝑥 ∈ 𝑉 ∧ (𝐷‘𝑥) = 𝐾)) |
4 | frgrwopreg.v | . . . . . . . . . . 11 ⊢ 𝑉 = (Vtx‘𝐺) | |
5 | 4 | vdgfrgrgt2 28076 | . . . . . . . . . 10 ⊢ ((𝐺 ∈ FriendGraph ∧ 𝑥 ∈ 𝑉) → (1 < (♯‘𝑉) → 2 ≤ ((VtxDeg‘𝐺)‘𝑥))) |
6 | 5 | imp 409 | . . . . . . . . 9 ⊢ (((𝐺 ∈ FriendGraph ∧ 𝑥 ∈ 𝑉) ∧ 1 < (♯‘𝑉)) → 2 ≤ ((VtxDeg‘𝐺)‘𝑥)) |
7 | breq2 5069 | . . . . . . . . . . 11 ⊢ (𝐾 = (𝐷‘𝑥) → (2 ≤ 𝐾 ↔ 2 ≤ (𝐷‘𝑥))) | |
8 | frgrwopreg.d | . . . . . . . . . . . . 13 ⊢ 𝐷 = (VtxDeg‘𝐺) | |
9 | 8 | fveq1i 6670 | . . . . . . . . . . . 12 ⊢ (𝐷‘𝑥) = ((VtxDeg‘𝐺)‘𝑥) |
10 | 9 | breq2i 5073 | . . . . . . . . . . 11 ⊢ (2 ≤ (𝐷‘𝑥) ↔ 2 ≤ ((VtxDeg‘𝐺)‘𝑥)) |
11 | 7, 10 | syl6bb 289 | . . . . . . . . . 10 ⊢ (𝐾 = (𝐷‘𝑥) → (2 ≤ 𝐾 ↔ 2 ≤ ((VtxDeg‘𝐺)‘𝑥))) |
12 | 11 | eqcoms 2829 | . . . . . . . . 9 ⊢ ((𝐷‘𝑥) = 𝐾 → (2 ≤ 𝐾 ↔ 2 ≤ ((VtxDeg‘𝐺)‘𝑥))) |
13 | 6, 12 | syl5ibrcom 249 | . . . . . . . 8 ⊢ (((𝐺 ∈ FriendGraph ∧ 𝑥 ∈ 𝑉) ∧ 1 < (♯‘𝑉)) → ((𝐷‘𝑥) = 𝐾 → 2 ≤ 𝐾)) |
14 | 13 | exp31 422 | . . . . . . 7 ⊢ (𝐺 ∈ FriendGraph → (𝑥 ∈ 𝑉 → (1 < (♯‘𝑉) → ((𝐷‘𝑥) = 𝐾 → 2 ≤ 𝐾)))) |
15 | 14 | com14 96 | . . . . . 6 ⊢ ((𝐷‘𝑥) = 𝐾 → (𝑥 ∈ 𝑉 → (1 < (♯‘𝑉) → (𝐺 ∈ FriendGraph → 2 ≤ 𝐾)))) |
16 | 15 | impcom 410 | . . . . 5 ⊢ ((𝑥 ∈ 𝑉 ∧ (𝐷‘𝑥) = 𝐾) → (1 < (♯‘𝑉) → (𝐺 ∈ FriendGraph → 2 ≤ 𝐾))) |
17 | 3, 16 | sylbi 219 | . . . 4 ⊢ (𝑥 ∈ 𝐴 → (1 < (♯‘𝑉) → (𝐺 ∈ FriendGraph → 2 ≤ 𝐾))) |
18 | 17 | exlimiv 1927 | . . 3 ⊢ (∃𝑥 𝑥 ∈ 𝐴 → (1 < (♯‘𝑉) → (𝐺 ∈ FriendGraph → 2 ≤ 𝐾))) |
19 | 1, 18 | sylbi 219 | . 2 ⊢ (𝐴 ≠ ∅ → (1 < (♯‘𝑉) → (𝐺 ∈ FriendGraph → 2 ≤ 𝐾))) |
20 | 19 | 3imp31 1108 | 1 ⊢ ((𝐺 ∈ FriendGraph ∧ 1 < (♯‘𝑉) ∧ 𝐴 ≠ ∅) → 2 ≤ 𝐾) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ↔ wb 208 ∧ wa 398 ∧ w3a 1083 = wceq 1533 ∃wex 1776 ∈ wcel 2110 ≠ wne 3016 {crab 3142 ∖ cdif 3932 ∅c0 4290 class class class wbr 5065 ‘cfv 6354 1c1 10537 < clt 10674 ≤ cle 10675 2c2 11691 ♯chash 13689 Vtxcvtx 26780 VtxDegcvtxdg 27246 FriendGraph cfrgr 28036 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1792 ax-4 1806 ax-5 1907 ax-6 1966 ax-7 2011 ax-8 2112 ax-9 2120 ax-10 2141 ax-11 2157 ax-12 2173 ax-ext 2793 ax-rep 5189 ax-sep 5202 ax-nul 5209 ax-pow 5265 ax-pr 5329 ax-un 7460 ax-cnex 10592 ax-resscn 10593 ax-1cn 10594 ax-icn 10595 ax-addcl 10596 ax-addrcl 10597 ax-mulcl 10598 ax-mulrcl 10599 ax-mulcom 10600 ax-addass 10601 ax-mulass 10602 ax-distr 10603 ax-i2m1 10604 ax-1ne0 10605 ax-1rid 10606 ax-rnegex 10607 ax-rrecex 10608 ax-cnre 10609 ax-pre-lttri 10610 ax-pre-lttrn 10611 ax-pre-ltadd 10612 ax-pre-mulgt0 10613 |
This theorem depends on definitions: df-bi 209 df-an 399 df-or 844 df-ifp 1058 df-3or 1084 df-3an 1085 df-tru 1536 df-ex 1777 df-nf 1781 df-sb 2066 df-mo 2618 df-eu 2650 df-clab 2800 df-cleq 2814 df-clel 2893 df-nfc 2963 df-ne 3017 df-nel 3124 df-ral 3143 df-rex 3144 df-reu 3145 df-rmo 3146 df-rab 3147 df-v 3496 df-sbc 3772 df-csb 3883 df-dif 3938 df-un 3940 df-in 3942 df-ss 3951 df-pss 3953 df-nul 4291 df-if 4467 df-pw 4540 df-sn 4567 df-pr 4569 df-tp 4571 df-op 4573 df-uni 4838 df-int 4876 df-iun 4920 df-br 5066 df-opab 5128 df-mpt 5146 df-tr 5172 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 7113 df-ov 7158 df-oprab 7159 df-mpo 7160 df-om 7580 df-1st 7688 df-2nd 7689 df-wrecs 7946 df-recs 8007 df-rdg 8045 df-1o 8101 df-oadd 8105 df-er 8288 df-map 8407 df-pm 8408 df-en 8509 df-dom 8510 df-sdom 8511 df-fin 8512 df-dju 9329 df-card 9367 df-pnf 10676 df-mnf 10677 df-xr 10678 df-ltxr 10679 df-le 10680 df-sub 10871 df-neg 10872 df-nn 11638 df-2 11699 df-3 11700 df-n0 11897 df-xnn0 11967 df-z 11981 df-uz 12243 df-xadd 12507 df-fz 12892 df-fzo 13033 df-hash 13690 df-word 13861 df-concat 13922 df-s1 13949 df-s2 14209 df-s3 14210 df-edg 26832 df-uhgr 26842 df-upgr 26866 df-umgr 26867 df-uspgr 26934 df-usgr 26935 df-vtxdg 27247 df-wlks 27380 df-wlkson 27381 df-trls 27473 df-trlson 27474 df-pths 27496 df-spths 27497 df-pthson 27498 df-spthson 27499 df-conngr 27965 df-frgr 28037 |
This theorem is referenced by: (None) |
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