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Mirrors > Home > MPE Home > Th. List > 1to3vfriendship | Structured version Visualization version GIF version |
Description: The friendship theorem for small graphs: In every friendship graph with one, two or three vertices, there is a vertex which is adjacent to all other vertices. (Contributed by Alexander van der Vekens, 6-Oct-2017.) (Revised by AV, 31-Mar-2021.) |
Ref | Expression |
---|---|
3vfriswmgr.v | ⊢ 𝑉 = (Vtx‘𝐺) |
3vfriswmgr.e | ⊢ 𝐸 = (Edg‘𝐺) |
Ref | Expression |
---|---|
1to3vfriendship | ⊢ ((𝐴 ∈ 𝑋 ∧ (𝑉 = {𝐴} ∨ 𝑉 = {𝐴, 𝐵} ∨ 𝑉 = {𝐴, 𝐵, 𝐶})) → (𝐺 ∈ FriendGraph → ∃𝑣 ∈ 𝑉 ∀𝑤 ∈ (𝑉 ∖ {𝑣}){𝑣, 𝑤} ∈ 𝐸)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 3vfriswmgr.v | . . 3 ⊢ 𝑉 = (Vtx‘𝐺) | |
2 | 3vfriswmgr.e | . . 3 ⊢ 𝐸 = (Edg‘𝐺) | |
3 | 1, 2 | 1to3vfriswmgr 28059 | . 2 ⊢ ((𝐴 ∈ 𝑋 ∧ (𝑉 = {𝐴} ∨ 𝑉 = {𝐴, 𝐵} ∨ 𝑉 = {𝐴, 𝐵, 𝐶})) → (𝐺 ∈ FriendGraph → ∃𝑣 ∈ 𝑉 ∀𝑤 ∈ (𝑉 ∖ {𝑣})({𝑤, 𝑣} ∈ 𝐸 ∧ ∃!𝑥 ∈ (𝑉 ∖ {𝑣}){𝑤, 𝑥} ∈ 𝐸))) |
4 | prcom 4668 | . . . . . . 7 ⊢ {𝑤, 𝑣} = {𝑣, 𝑤} | |
5 | 4 | eleq1i 2903 | . . . . . 6 ⊢ ({𝑤, 𝑣} ∈ 𝐸 ↔ {𝑣, 𝑤} ∈ 𝐸) |
6 | 5 | biimpi 218 | . . . . 5 ⊢ ({𝑤, 𝑣} ∈ 𝐸 → {𝑣, 𝑤} ∈ 𝐸) |
7 | 6 | adantr 483 | . . . 4 ⊢ (({𝑤, 𝑣} ∈ 𝐸 ∧ ∃!𝑥 ∈ (𝑉 ∖ {𝑣}){𝑤, 𝑥} ∈ 𝐸) → {𝑣, 𝑤} ∈ 𝐸) |
8 | 7 | ralimi 3160 | . . 3 ⊢ (∀𝑤 ∈ (𝑉 ∖ {𝑣})({𝑤, 𝑣} ∈ 𝐸 ∧ ∃!𝑥 ∈ (𝑉 ∖ {𝑣}){𝑤, 𝑥} ∈ 𝐸) → ∀𝑤 ∈ (𝑉 ∖ {𝑣}){𝑣, 𝑤} ∈ 𝐸) |
9 | 8 | reximi 3243 | . 2 ⊢ (∃𝑣 ∈ 𝑉 ∀𝑤 ∈ (𝑉 ∖ {𝑣})({𝑤, 𝑣} ∈ 𝐸 ∧ ∃!𝑥 ∈ (𝑉 ∖ {𝑣}){𝑤, 𝑥} ∈ 𝐸) → ∃𝑣 ∈ 𝑉 ∀𝑤 ∈ (𝑉 ∖ {𝑣}){𝑣, 𝑤} ∈ 𝐸) |
10 | 3, 9 | syl6 35 | 1 ⊢ ((𝐴 ∈ 𝑋 ∧ (𝑉 = {𝐴} ∨ 𝑉 = {𝐴, 𝐵} ∨ 𝑉 = {𝐴, 𝐵, 𝐶})) → (𝐺 ∈ FriendGraph → ∃𝑣 ∈ 𝑉 ∀𝑤 ∈ (𝑉 ∖ {𝑣}){𝑣, 𝑤} ∈ 𝐸)) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 398 ∨ w3o 1082 = wceq 1537 ∈ wcel 2114 ∀wral 3138 ∃wrex 3139 ∃!wreu 3140 ∖ cdif 3933 {csn 4567 {cpr 4569 {ctp 4571 ‘cfv 6355 Vtxcvtx 26781 Edgcedg 26832 FriendGraph cfrgr 28037 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1796 ax-4 1810 ax-5 1911 ax-6 1970 ax-7 2015 ax-8 2116 ax-9 2124 ax-10 2145 ax-11 2161 ax-12 2177 ax-ext 2793 ax-rep 5190 ax-sep 5203 ax-nul 5210 ax-pow 5266 ax-pr 5330 ax-un 7461 ax-cnex 10593 ax-resscn 10594 ax-1cn 10595 ax-icn 10596 ax-addcl 10597 ax-addrcl 10598 ax-mulcl 10599 ax-mulrcl 10600 ax-mulcom 10601 ax-addass 10602 ax-mulass 10603 ax-distr 10604 ax-i2m1 10605 ax-1ne0 10606 ax-1rid 10607 ax-rnegex 10608 ax-rrecex 10609 ax-cnre 10610 ax-pre-lttri 10611 ax-pre-lttrn 10612 ax-pre-ltadd 10613 ax-pre-mulgt0 10614 |
This theorem depends on definitions: df-bi 209 df-an 399 df-or 844 df-3or 1084 df-3an 1085 df-tru 1540 df-ex 1781 df-nf 1785 df-sb 2070 df-mo 2622 df-eu 2654 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 3773 df-csb 3884 df-dif 3939 df-un 3941 df-in 3943 df-ss 3952 df-pss 3954 df-nul 4292 df-if 4468 df-pw 4541 df-sn 4568 df-pr 4570 df-tp 4572 df-op 4574 df-uni 4839 df-int 4877 df-iun 4921 df-br 5067 df-opab 5129 df-mpt 5147 df-tr 5173 df-id 5460 df-eprel 5465 df-po 5474 df-so 5475 df-fr 5514 df-we 5516 df-xp 5561 df-rel 5562 df-cnv 5563 df-co 5564 df-dm 5565 df-rn 5566 df-res 5567 df-ima 5568 df-pred 6148 df-ord 6194 df-on 6195 df-lim 6196 df-suc 6197 df-iota 6314 df-fun 6357 df-fn 6358 df-f 6359 df-f1 6360 df-fo 6361 df-f1o 6362 df-fv 6363 df-riota 7114 df-ov 7159 df-oprab 7160 df-mpo 7161 df-om 7581 df-1st 7689 df-2nd 7690 df-wrecs 7947 df-recs 8008 df-rdg 8046 df-1o 8102 df-oadd 8106 df-er 8289 df-en 8510 df-dom 8511 df-sdom 8512 df-fin 8513 df-dju 9330 df-card 9368 df-pnf 10677 df-mnf 10678 df-xr 10679 df-ltxr 10680 df-le 10681 df-sub 10872 df-neg 10873 df-nn 11639 df-2 11701 df-n0 11899 df-z 11983 df-uz 12245 df-fz 12894 df-hash 13692 df-edg 26833 df-umgr 26868 df-usgr 26936 df-frgr 28038 |
This theorem is referenced by: friendship 28178 |
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