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Theorem numclwlk1 30225
Description: Statement 9 in [Huneke] p. 2: "If n > 1, then the number of closed n-walks v(0) ... v(n-2) v(n-1) v(n) from v = v(0) = v(n) with v(n-2) = v is kf(n-2)". Since 𝐺 is k-regular, the vertex v(n-2) = v has k neighbors v(n-1), so there are k walks from v(n-2) = v to v(n) = v (via each of v's neighbors) completing each of the f(n-2) walks from v=v(0) to v(n-2)=v. This theorem holds even for k=0. (Contributed by AV, 23-May-2022.)
Hypotheses
Ref Expression
numclwlk1.v 𝑉 = (Vtxβ€˜πΊ)
numclwlk1.c 𝐢 = {𝑀 ∈ (ClWalksβ€˜πΊ) ∣ ((β™―β€˜(1st β€˜π‘€)) = 𝑁 ∧ ((2nd β€˜π‘€)β€˜0) = 𝑋 ∧ ((2nd β€˜π‘€)β€˜(𝑁 βˆ’ 2)) = 𝑋)}
numclwlk1.f 𝐹 = {𝑀 ∈ (ClWalksβ€˜πΊ) ∣ ((β™―β€˜(1st β€˜π‘€)) = (𝑁 βˆ’ 2) ∧ ((2nd β€˜π‘€)β€˜0) = 𝑋)}
Assertion
Ref Expression
numclwlk1 (((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) ∧ (𝑋 ∈ 𝑉 ∧ 𝑁 ∈ (β„€β‰₯β€˜2))) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))
Distinct variable groups:   𝑀,𝐺   𝑀,𝐾   𝑀,𝑁   𝑀,𝑉   𝑀,𝑋   𝑀,𝐢   𝑀,𝐹

Proof of Theorem numclwlk1
StepHypRef Expression
1 uzp1 12893 . . . 4 (𝑁 ∈ (β„€β‰₯β€˜2) β†’ (𝑁 = 2 ∨ 𝑁 ∈ (β„€β‰₯β€˜(2 + 1))))
2 numclwlk1.v . . . . . . . 8 𝑉 = (Vtxβ€˜πΊ)
3 numclwlk1.c . . . . . . . 8 𝐢 = {𝑀 ∈ (ClWalksβ€˜πΊ) ∣ ((β™―β€˜(1st β€˜π‘€)) = 𝑁 ∧ ((2nd β€˜π‘€)β€˜0) = 𝑋 ∧ ((2nd β€˜π‘€)β€˜(𝑁 βˆ’ 2)) = 𝑋)}
4 numclwlk1.f . . . . . . . 8 𝐹 = {𝑀 ∈ (ClWalksβ€˜πΊ) ∣ ((β™―β€˜(1st β€˜π‘€)) = (𝑁 βˆ’ 2) ∧ ((2nd β€˜π‘€)β€˜0) = 𝑋)}
52, 3, 4numclwlk1lem1 30223 . . . . . . 7 (((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) ∧ (𝑋 ∈ 𝑉 ∧ 𝑁 = 2)) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))
65expcom 412 . . . . . 6 ((𝑋 ∈ 𝑉 ∧ 𝑁 = 2) β†’ ((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ))))
76expcom 412 . . . . 5 (𝑁 = 2 β†’ (𝑋 ∈ 𝑉 β†’ ((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))))
82, 3, 4numclwlk1lem2 30224 . . . . . . . 8 (((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) ∧ (𝑋 ∈ 𝑉 ∧ 𝑁 ∈ (β„€β‰₯β€˜3))) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))
98expcom 412 . . . . . . 7 ((𝑋 ∈ 𝑉 ∧ 𝑁 ∈ (β„€β‰₯β€˜3)) β†’ ((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ))))
109expcom 412 . . . . . 6 (𝑁 ∈ (β„€β‰₯β€˜3) β†’ (𝑋 ∈ 𝑉 β†’ ((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))))
11 2p1e3 12384 . . . . . . 7 (2 + 1) = 3
1211fveq2i 6895 . . . . . 6 (β„€β‰₯β€˜(2 + 1)) = (β„€β‰₯β€˜3)
1310, 12eleq2s 2843 . . . . 5 (𝑁 ∈ (β„€β‰₯β€˜(2 + 1)) β†’ (𝑋 ∈ 𝑉 β†’ ((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))))
147, 13jaoi 855 . . . 4 ((𝑁 = 2 ∨ 𝑁 ∈ (β„€β‰₯β€˜(2 + 1))) β†’ (𝑋 ∈ 𝑉 β†’ ((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))))
151, 14syl 17 . . 3 (𝑁 ∈ (β„€β‰₯β€˜2) β†’ (𝑋 ∈ 𝑉 β†’ ((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))))
1615impcom 406 . 2 ((𝑋 ∈ 𝑉 ∧ 𝑁 ∈ (β„€β‰₯β€˜2)) β†’ ((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ))))
1716impcom 406 1 (((𝑉 ∈ Fin ∧ 𝐺 RegUSGraph 𝐾) ∧ (𝑋 ∈ 𝑉 ∧ 𝑁 ∈ (β„€β‰₯β€˜2))) β†’ (β™―β€˜πΆ) = (𝐾 Β· (β™―β€˜πΉ)))
Colors of variables: wff setvar class
Syntax hints:   β†’ wi 4   ∧ wa 394   ∨ wo 845   ∧ w3a 1084   = wceq 1533   ∈ wcel 2098  {crab 3419   class class class wbr 5143  β€˜cfv 6543  (class class class)co 7416  1st c1st 7989  2nd c2nd 7990  Fincfn 8962  0cc0 11138  1c1 11139   + caddc 11141   Β· cmul 11143   βˆ’ cmin 11474  2c2 12297  3c3 12298  β„€β‰₯cuz 12852  β™―chash 14321  Vtxcvtx 28853   RegUSGraph crusgr 29414  ClWalkscclwlks 29628
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 5280  ax-sep 5294  ax-nul 5301  ax-pow 5359  ax-pr 5423  ax-un 7738  ax-cnex 11194  ax-resscn 11195  ax-1cn 11196  ax-icn 11197  ax-addcl 11198  ax-addrcl 11199  ax-mulcl 11200  ax-mulrcl 11201  ax-mulcom 11202  ax-addass 11203  ax-mulass 11204  ax-distr 11205  ax-i2m1 11206  ax-1ne0 11207  ax-1rid 11208  ax-rnegex 11209  ax-rrecex 11210  ax-cnre 11211  ax-pre-lttri 11212  ax-pre-lttrn 11213  ax-pre-ltadd 11214  ax-pre-mulgt0 11215
This theorem depends on definitions:  df-bi 206  df-an 395  df-or 846  df-ifp 1061  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 3769  df-csb 3885  df-dif 3942  df-un 3944  df-in 3946  df-ss 3956  df-pss 3959  df-nul 4319  df-if 4525  df-pw 4600  df-sn 4625  df-pr 4627  df-op 4631  df-uni 4904  df-int 4945  df-iun 4993  df-br 5144  df-opab 5206  df-mpt 5227  df-tr 5261  df-id 5570  df-eprel 5576  df-po 5584  df-so 5585  df-fr 5627  df-we 5629  df-xp 5678  df-rel 5679  df-cnv 5680  df-co 5681  df-dm 5682  df-rn 5683  df-res 5684  df-ima 5685  df-pred 6300  df-ord 6367  df-on 6368  df-lim 6369  df-suc 6370  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 7372  df-ov 7419  df-oprab 7420  df-mpo 7421  df-om 7869  df-1st 7991  df-2nd 7992  df-frecs 8285  df-wrecs 8316  df-recs 8390  df-rdg 8429  df-1o 8485  df-2o 8486  df-oadd 8489  df-er 8723  df-map 8845  df-pm 8846  df-en 8963  df-dom 8964  df-sdom 8965  df-fin 8966  df-dju 9924  df-card 9962  df-pnf 11280  df-mnf 11281  df-xr 11282  df-ltxr 11283  df-le 11284  df-sub 11476  df-neg 11477  df-nn 12243  df-2 12305  df-3 12306  df-n0 12503  df-xnn0 12575  df-z 12589  df-uz 12853  df-rp 13007  df-xadd 13125  df-fz 13517  df-fzo 13660  df-seq 13999  df-exp 14059  df-hash 14322  df-word 14497  df-lsw 14545  df-concat 14553  df-s1 14578  df-substr 14623  df-pfx 14653  df-s2 14831  df-vtx 28855  df-iedg 28856  df-edg 28905  df-uhgr 28915  df-ushgr 28916  df-upgr 28939  df-umgr 28940  df-uspgr 29007  df-usgr 29008  df-fusgr 29174  df-nbgr 29190  df-vtxdg 29324  df-rgr 29415  df-rusgr 29416  df-wlks 29457  df-clwlks 29629  df-wwlks 29685  df-wwlksn 29686  df-clwwlk 29836  df-clwwlkn 29879  df-clwwlknon 29942
This theorem is referenced by: (None)
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