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Mirrors > Home > MPE Home > Th. List > 2pthfrgrrn2 | Structured version Visualization version GIF version |
Description: Between any two (different) vertices in a friendship graph is a 2-path (path of length 2), see Proposition 1(b) of [MertziosUnger] p. 153 : "A friendship graph G ..., as well as the distance between any two nodes in G is at most two". (Contributed by Alexander van der Vekens, 16-Nov-2017.) (Revised by AV, 1-Apr-2021.) |
Ref | Expression |
---|---|
2pthfrgrrn.v | ⊢ 𝑉 = (Vtx‘𝐺) |
2pthfrgrrn.e | ⊢ 𝐸 = (Edg‘𝐺) |
Ref | Expression |
---|---|
2pthfrgrrn2 | ⊢ (𝐺 ∈ FriendGraph → ∀𝑎 ∈ 𝑉 ∀𝑐 ∈ (𝑉 ∖ {𝑎})∃𝑏 ∈ 𝑉 (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) ∧ (𝑎 ≠ 𝑏 ∧ 𝑏 ≠ 𝑐))) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 2pthfrgrrn.v | . . 3 ⊢ 𝑉 = (Vtx‘𝐺) | |
2 | 2pthfrgrrn.e | . . 3 ⊢ 𝐸 = (Edg‘𝐺) | |
3 | 1, 2 | 2pthfrgrrn 28221 | . 2 ⊢ (𝐺 ∈ FriendGraph → ∀𝑎 ∈ 𝑉 ∀𝑐 ∈ (𝑉 ∖ {𝑎})∃𝑏 ∈ 𝑉 ({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸)) |
4 | frgrusgr 28200 | . . . . . . 7 ⊢ (𝐺 ∈ FriendGraph → 𝐺 ∈ USGraph) | |
5 | 2 | usgredgne 27150 | . . . . . . . . 9 ⊢ ((𝐺 ∈ USGraph ∧ {𝑎, 𝑏} ∈ 𝐸) → 𝑎 ≠ 𝑏) |
6 | 5 | ex 416 | . . . . . . . 8 ⊢ (𝐺 ∈ USGraph → ({𝑎, 𝑏} ∈ 𝐸 → 𝑎 ≠ 𝑏)) |
7 | 2 | usgredgne 27150 | . . . . . . . . 9 ⊢ ((𝐺 ∈ USGraph ∧ {𝑏, 𝑐} ∈ 𝐸) → 𝑏 ≠ 𝑐) |
8 | 7 | ex 416 | . . . . . . . 8 ⊢ (𝐺 ∈ USGraph → ({𝑏, 𝑐} ∈ 𝐸 → 𝑏 ≠ 𝑐)) |
9 | 6, 8 | anim12d 612 | . . . . . . 7 ⊢ (𝐺 ∈ USGraph → (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) → (𝑎 ≠ 𝑏 ∧ 𝑏 ≠ 𝑐))) |
10 | 4, 9 | syl 17 | . . . . . 6 ⊢ (𝐺 ∈ FriendGraph → (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) → (𝑎 ≠ 𝑏 ∧ 𝑏 ≠ 𝑐))) |
11 | 10 | ad2antrr 726 | . . . . 5 ⊢ (((𝐺 ∈ FriendGraph ∧ (𝑎 ∈ 𝑉 ∧ 𝑐 ∈ (𝑉 ∖ {𝑎}))) ∧ 𝑏 ∈ 𝑉) → (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) → (𝑎 ≠ 𝑏 ∧ 𝑏 ≠ 𝑐))) |
12 | 11 | ancld 554 | . . . 4 ⊢ (((𝐺 ∈ FriendGraph ∧ (𝑎 ∈ 𝑉 ∧ 𝑐 ∈ (𝑉 ∖ {𝑎}))) ∧ 𝑏 ∈ 𝑉) → (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) → (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) ∧ (𝑎 ≠ 𝑏 ∧ 𝑏 ≠ 𝑐)))) |
13 | 12 | reximdva 3184 | . . 3 ⊢ ((𝐺 ∈ FriendGraph ∧ (𝑎 ∈ 𝑉 ∧ 𝑐 ∈ (𝑉 ∖ {𝑎}))) → (∃𝑏 ∈ 𝑉 ({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) → ∃𝑏 ∈ 𝑉 (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) ∧ (𝑎 ≠ 𝑏 ∧ 𝑏 ≠ 𝑐)))) |
14 | 13 | ralimdvva 3093 | . 2 ⊢ (𝐺 ∈ FriendGraph → (∀𝑎 ∈ 𝑉 ∀𝑐 ∈ (𝑉 ∖ {𝑎})∃𝑏 ∈ 𝑉 ({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) → ∀𝑎 ∈ 𝑉 ∀𝑐 ∈ (𝑉 ∖ {𝑎})∃𝑏 ∈ 𝑉 (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) ∧ (𝑎 ≠ 𝑏 ∧ 𝑏 ≠ 𝑐)))) |
15 | 3, 14 | mpd 15 | 1 ⊢ (𝐺 ∈ FriendGraph → ∀𝑎 ∈ 𝑉 ∀𝑐 ∈ (𝑉 ∖ {𝑎})∃𝑏 ∈ 𝑉 (({𝑎, 𝑏} ∈ 𝐸 ∧ {𝑏, 𝑐} ∈ 𝐸) ∧ (𝑎 ≠ 𝑏 ∧ 𝑏 ≠ 𝑐))) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 399 = wceq 1542 ∈ wcel 2114 ≠ wne 2934 ∀wral 3053 ∃wrex 3054 ∖ cdif 3840 {csn 4516 {cpr 4518 ‘cfv 6339 Vtxcvtx 26943 Edgcedg 26994 USGraphcusgr 27096 FriendGraph cfrgr 28197 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1802 ax-4 1816 ax-5 1917 ax-6 1975 ax-7 2020 ax-8 2116 ax-9 2124 ax-10 2145 ax-11 2162 ax-12 2179 ax-ext 2710 ax-sep 5167 ax-nul 5174 ax-pow 5232 ax-pr 5296 ax-un 7481 ax-cnex 10673 ax-resscn 10674 ax-1cn 10675 ax-icn 10676 ax-addcl 10677 ax-addrcl 10678 ax-mulcl 10679 ax-mulrcl 10680 ax-mulcom 10681 ax-addass 10682 ax-mulass 10683 ax-distr 10684 ax-i2m1 10685 ax-1ne0 10686 ax-1rid 10687 ax-rnegex 10688 ax-rrecex 10689 ax-cnre 10690 ax-pre-lttri 10691 ax-pre-lttrn 10692 ax-pre-ltadd 10693 ax-pre-mulgt0 10694 |
This theorem depends on definitions: df-bi 210 df-an 400 df-or 847 df-3or 1089 df-3an 1090 df-tru 1545 df-fal 1555 df-ex 1787 df-nf 1791 df-sb 2075 df-mo 2540 df-eu 2570 df-clab 2717 df-cleq 2730 df-clel 2811 df-nfc 2881 df-ne 2935 df-nel 3039 df-ral 3058 df-rex 3059 df-reu 3060 df-rmo 3061 df-rab 3062 df-v 3400 df-sbc 3681 df-csb 3791 df-dif 3846 df-un 3848 df-in 3850 df-ss 3860 df-pss 3862 df-nul 4212 df-if 4415 df-pw 4490 df-sn 4517 df-pr 4519 df-tp 4521 df-op 4523 df-uni 4797 df-int 4837 df-iun 4883 df-br 5031 df-opab 5093 df-mpt 5111 df-tr 5137 df-id 5429 df-eprel 5434 df-po 5442 df-so 5443 df-fr 5483 df-we 5485 df-xp 5531 df-rel 5532 df-cnv 5533 df-co 5534 df-dm 5535 df-rn 5536 df-res 5537 df-ima 5538 df-pred 6129 df-ord 6175 df-on 6176 df-lim 6177 df-suc 6178 df-iota 6297 df-fun 6341 df-fn 6342 df-f 6343 df-f1 6344 df-fo 6345 df-f1o 6346 df-fv 6347 df-riota 7129 df-ov 7175 df-oprab 7176 df-mpo 7177 df-om 7602 df-1st 7716 df-2nd 7717 df-wrecs 7978 df-recs 8039 df-rdg 8077 df-1o 8133 df-oadd 8137 df-er 8322 df-en 8558 df-dom 8559 df-sdom 8560 df-fin 8561 df-dju 9405 df-card 9443 df-pnf 10757 df-mnf 10758 df-xr 10759 df-ltxr 10760 df-le 10761 df-sub 10952 df-neg 10953 df-nn 11719 df-2 11781 df-n0 11979 df-z 12065 df-uz 12327 df-fz 12984 df-hash 13785 df-edg 26995 df-umgr 27030 df-usgr 27098 df-frgr 28198 |
This theorem is referenced by: 2pthfrgr 28223 3cyclfrgrrn1 28224 |
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