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Stallings theorem about ends of groups

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gave a proof based on the ideas of edge-cuts. Later Dunwoody also gave a proof of Stallings' theorem for finitely presented groups using the method of "tracks" on finite 2-complexes. Niblo obtained a proof of Stallings' theorem as a consequence of Sageev's CAT(0)-cubing relative version, where the
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stabilizes an essential "hyperplane" (a simplicial tree is an example of a CAT(0)-cubing where the hyperplanes are the midpoints of edges). In certain situations such a semi-splitting can be promoted to an actual algebraic splitting, typically over a subgroup commensurable with
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that are not accessible. Linnell showed that if one bounds the size of finite subgroups over which the splittings are taken then every finitely generated group is accessible in this sense as well. These results in turn gave rise to other versions of accessibility such as
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outlined a proof (see pp. 228–230 in ) where the minimal surfaces argument is replaced by an easier harmonic analysis argument and this approach was pushed further by Kapovich to cover the original case of finitely generated
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Among the immediate applications of Stallings' theorem was a proof by Stallings of a long-standing conjecture that every finitely generated group of cohomological dimension one is free and that every torsion-free
5477:. Early work on semi-splittings, inspired by Stallings' theorem, was done in the 1970s and 1980s by Scott, Swarup, and others. The work of Sageev and Gerasimov in the 1990s showed that for a subgroup 4617: 4153: 4977:
since the number of ends of a finitely generated group is easily seen to be a quasi-isometry invariant. For this reason Stallings' theorem is considered to be one of the first results in
2075: 898: 1853: 2746: 718: 657: 547: 480: 320: 3539: 2398: 1506: 1929: 1774: 1085: 753: 512: 1809: 1973: 1550: 6226:(in Russian) Algebra, geometry, analysis and mathematical physics (Novosibirsk, 1996), pp. 91–109, 190, Izdat. Ross. Akad. Nauk Sib. Otd. Inst. Mat., Novosibirsk, 1997 5501: 5292: 4851: 2954: 2590: 2468: 2333: 1737: 1380: 1321: 1217: 1151: 1004: 683: 582: 445: 265: 5883:. Geometric group theory, Vol. 1 (Sussex, 1991), pp. 75–78, London Mathematical Society Lecture Note Series, vol. 181, Cambridge University Press, Cambridge, 1993; 5542: 5435: 5097:-Feighn accessibility of finitely presented groups (where the so-called "small" splittings are considered), acylindrical accessibility, strong accessibility, and others. 837: 782: 4761: 4431: 4368: 4294: 4068: 3917: 3848: 3813: 3478: 3366: 3222: 3183: 3070: 2874: 2788: 1243: 1030: 386: 2835: 2620: 4507: 4481: 3993: 3967: 2812: 2660: 1191: 1125: 978: 938: 857: 805: 360: 285: 228: 200: 176: 5350: 2984: 2136: 1689: 4907: 4671: 4644: 4211: 4184: 3754: 3702: 3655: 3263: 3117: 2925: 2707: 2495: 5807:
A James K. Whittemore Lecture in Mathematics given at Yale University, 1969. Yale Mathematical Monographs, 4. Yale University Press, New Haven, Conn.-London, 1971.
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CAT(0)-cubing is eventually promoted to being a tree. Niblo's paper also defines an abstract group-theoretic obstruction (which is a union of double cosets of
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is finite (Stallings' theorem). Another situation where an actual splitting can be obtained (modulo a few exceptions) is for semi-splittings over virtually
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Lemma 4.1 in C. T. C. Wall, Poincaré Complexes: I. Annals of Mathematics, Second Series, Vol. 86, No. 2 (Sep., 1967), pp. 213-245
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with respect to virtually polycyclic subgroups is dealt with by the algebraic torus theorem of Dunwoody-Swenson.
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H. Hopf. Enden offener Räume und unendliche diskontinuierliche Gruppen. Comment. Math. Helv. 16, (1944). 81-100
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Stallings' theorem also implies that the property of having a nontrivial splitting over a finite subgroup is a
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M. Gromov, Hyperbolic Groups, in "Essays in Group Theory" (G. M. Gersten, ed.), MSRI Publ. 8, 1987, pp. 75-263
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A number of new proofs of Stallings' theorem have been obtained by others after Stallings' original proof.
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Using Dunwoody's accessibility result, Stallings' theorem about ends of groups and the fact that if
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H. Freudenthal. Über die Enden diskreter Räume und Gruppen. Comment. Math. Helv. 17, (1945). 1-38.
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UniversitĂ© de Grenoble. Annales de l'Institut Fourier, vol. 49 (1999), no. 4, pp. 1215–1224
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Proceedings of the London Mathematical Society (3), vol. 71 (1995), no. 3, pp. 585–617
5707:, where one first realizes a finitely presented group as the fundamental group of a compact 5320: 2963: 2106: 1659: 6194: 6144: 6103: 6026: 5927: 4880: 4649: 4622: 4189: 4162: 3727: 3680: 3628: 3236: 3095: 2987: 2903: 2685: 2473: 1863: 1598: 8: 6314: 6309: 5700: 4788: 2500: 2247: 2190: 130: 5637:
over two-ended (virtually infinite cyclic) subgroups was treated by Scott-Swarup and by
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Bulletin of the American Mathematical Society, vol. 74 (1968), pp. 361–364
5727:-manifold (see, for example, a sketch of this argument in the survey article of 5638: 4970: 231: 6355: 6173:
Kropholler, P. H.; Roller, M. A. (1989). "Relative ends and duality groups".
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http://www.ams.org/journals/proc/2008-136-12/S0002-9939-08-08973-9/home.html
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Journal of Pure and Applied Algebra, vol. 89 (1993), no. 1-2, pp. 3–47
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Stallings' theorem is a key tool in proving that a finitely generated group
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is virtually infinite cyclic if and only if it has a finite normal subgroup
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A geometric proof of Stallings' theorem on groups with more than one end.
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Pacific Journal of Mathematics, vol. 196 (2000), no. 2, pp. 461–506
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over finite subgroups always terminates in a finite number of steps. In
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of this topological space. A more explicit definition of the number of
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Energy of harmonic functions and Gromov's proof of Stallings' theorem
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Revista Matemática Complutense vol. 16(2003), no. 1, pp. 5–101
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Mathematische Zeitschrift, vol. 176 (1981), no. 2, pp. 223–246
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Gentimis Thanos, Asymptotic dimension of finitely presented groups,
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with respect to subgroups have also been considered. For a subgroup
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Sur l'accessibilité acylindrique des groupes de présentation finie.
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with finite edge groups is bounded by some constant depending on
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where all vertex and edge groups are finite (see, for example,).
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is a finitely presented group with asymptotic dimension 1 then
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is virtually free one can show that for a finitely presented
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Ends of group pairs and non-positively curved cube complexes.
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Bounding the complexity of simplicial group actions on trees.
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Relative versions of Stallings' theorem and relative ends of
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admits a nontrivial (that is, without a global fixed vertex)
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are almost invariant (equivalently, if and only if the set
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admits a nontrivial (that is, without a global fixed point)
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with finite edge-stabilizers and without edge-inversions.
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with finite edge-stabilizers and without edge-inversions.
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Cut points and canonical splittings of hyperbolic groups.
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terms that the number of edges in a reduced splitting of
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Stallings' theorem shows that the converse is also true.
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A more precise version of this argument shows that for a
3228: 1508:. A basic fact in the theory of ends of groups says that 182:
where the degree of every vertex is finite. One can view
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as the number of ends of the relative Cayley graph (the
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can be represented as the fundamental group of a finite
4612:{\displaystyle G=\langle H,t|t^{-1}C_{1}t=C_{2}\rangle } 4148:{\displaystyle G=\langle H,t|t^{-1}C_{1}t=C_{2}\rangle } 206:
by giving it the natural structure of a one-dimensional
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Stallings' theorem was a starting point for Dunwoody's
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consist of the trivial element and all the elements of
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if and only if there exists at least one essential cut
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is the number of "connected components at infinity" of
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The geometry of abstract groups and their splittings.
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Scott, Peter (1977–1978). "Ends of pairs of groups".
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Combinatorica, vol. 2 (1982), no. 1, pp. 15–23
5012:if the process of iterated nontrivial splitting of 4952: 1991:established in the 1940s the following two facts: 5719: 5687: 5667: 5621: 5601: 5580: 5556: 5536: 5495: 5469: 5449: 5429: 5388: 5368: 5344: 5306: 5286: 5253: 5229: 5209: 5186: 5166: 5139: 5112: 5072: 5048: 5024: 5000: 4941: 4921: 4901: 4865: 4845: 4806: 4775: 4755: 4720: 4689: 4665: 4638: 4611: 4525: 4501: 4475: 4449: 4425: 4386: 4362: 4320: 4288: 4249: 4229: 4205: 4178: 4147: 4062: 4027: 4007: 3987: 3961: 3935: 3911: 3868: 3842: 3807: 3768: 3748: 3716: 3696: 3669: 3649: 3617: 3597: 3577: 3557: 3533: 3492: 3472: 3440: 3420: 3400: 3380: 3360: 3325: 3297: 3277: 3257: 3216: 3177: 3131: 3111: 3084: 3064: 3025: 3002: 2978: 2948: 2919: 2892: 2868: 2829: 2806: 2782: 2740: 2701: 2674: 2654: 2634: 2614: 2584: 2555: 2535: 2515: 2489: 2462: 2436: 2416: 2392: 2351: 2327: 2297: 2264: 2236: 2216: 2177: 2150: 2130: 2095: 2069: 2010: 1967: 1923: 1881: 1847: 1803: 1768: 1731: 1703: 1683: 1648: 1616: 1587: 1567: 1544: 1500: 1441: 1418: 1398: 1374: 1339: 1315: 1285: 1257: 1237: 1211: 1185: 1165: 1145: 1119: 1099: 1079: 1044: 1024: 998: 972: 952: 932: 912: 892: 851: 831: 799: 776: 747: 712: 677: 651: 616: 596: 576: 541: 506: 474: 439: 400: 380: 354: 334: 314: 279: 259: 222: 194: 170: 117: 97: 60: 39: 6224:Semi-splittings of groups and actions on cubings. 5998: 5788:On torsion-free groups with infinitely many ends. 2280: 2200:proved in 1967 the following complementary fact: 144:case (1968) and then in the general case (1971). 85:the theorem says that a finitely generated group 6353: 6172: 5864:The accessibility of finitely presented groups. 5633:subgroups. Here the case of semi-splittings of 47:has more than one end if and only if the group 4705:this result can be restated as follows: For a 5805:Group theory and three-dimensional manifolds. 5564:admitting an essential isometric action on a 6119:"Relative version of a theorem of Stallings" 5999:Delzant, Thomas; Potyagailo, Leonid (2001). 4606: 4550: 4142: 4086: 2064: 2040: 1979: 6284:, vol. 140 (2000), no. 3, pp. 605–637 6266:, vol. 180 (1998), no. 2, pp. 145–186 6116: 5967:, vol. 129 (1997), no. 3, pp. 527–565 5949:, vol. 103 (1991), no. 3, pp. 449–469 4370:if and only if one of the following holds: 3147:A simple but important observation states: 1627: 6081: 1552:does not depend on the choice of a finite 6134: 6016: 5917: 3333:has at least one essential cut and hence 2070:{\displaystyle e(G)\in \{0,1,2,\infty \}} 1826: 1791: 1753: 1725: 69:admits a nontrivial decomposition as an 6160:Decomposition theorems for group pairs. 5899: 5846:Groups of dimension 1 are locally free. 2642:consists of all (topological) edges of 893:{\displaystyle e(\Gamma )=m<\infty } 6354: 6053: 6051: 5961:Acylindrical accessibility for groups. 5794:(2), vol. 88 (1968), pp. 312–334 5088:is accessible but that there do exist 4304:Formal statement of Stallings' theorem 3229:Cuts and splittings over finite groups 1848:{\displaystyle e(\mathbb {Z} ^{2})=1.} 22:Stallings theorem about ends of groups 6068: 6066: 6042:Covering theory for graphs of groups. 2741:{\displaystyle \delta A=\delta A^{*}} 713:{\displaystyle e(\Gamma )\leqslant n} 659:. If there does not exist an integer 652:{\displaystyle e(\Gamma )\leqslant n} 542:{\displaystyle e(\Gamma )\leqslant n} 475:{\displaystyle e(\Gamma )\leqslant m} 315:{\displaystyle e(\Gamma )\leqslant n} 267:be a non-negative integer. The graph 238:is presented below for completeness. 105:has more than one end if and only if 5870:, vol. 81 (1985), no. 3, pp. 449-457 5568:where a subgroup commensurable with 3756:starts with a nontrivial element of 3657:starts with a nontrivial element of 3534:{\displaystyle \Gamma =\Gamma (G,S)} 2393:{\displaystyle \Gamma =\Gamma (G,S)} 1501:{\displaystyle e(G)=e(\Gamma (G,S))} 604:is the smallest nonnegative integer 6275:M. J. Dunwoody, and E. L. Swenson. 6175:Journal of Pure and Applied Algebra 6123:Journal of Pure and Applied Algebra 6084:Journal of Pure and Applied Algebra 6048: 5906:Journal of Pure and Applied Algebra 5857: 5855: 3033:is finite. It is easy to see that 1924:{\displaystyle 1<|X|<\infty } 1052:infinite connected components. If 13: 6317:, vol. 105 (2004), pp. 61–76 6063: 4840: 4818:, Stallings' theorem implies that 3724:whose normal form expressions for 3625:whose normal form expressions for 3513: 3507: 2801: 2649: 2372: 2366: 2061: 1962: 1918: 1769:{\displaystyle e(\mathbb {Z} )=2.} 1521: 1477: 1354: 1226: 1180: 1114: 1080:{\displaystyle e(\Gamma )=\infty } 1074: 1065: 1013: 967: 927: 887: 872: 846: 823: 794: 768: 748:{\displaystyle e(\Gamma )=\infty } 742: 733: 698: 637: 562: 527: 460: 425: 369: 349: 300: 274: 217: 189: 165: 14: 6378: 6345:, preprint, 2007, arXiv:0707.4231 5641:. The case of semi-splittings of 3815:is an essential cut in Γ so that 3072:is a cut if and only if the sets 1268: 507:{\displaystyle 0\leqslant n<m} 147: 5852: 4953:Applications and generalizations 3142: 1804:{\displaystyle \mathbb {Z} ^{2}} 6333: 6320: 6302: 6287: 6269: 6251: 6235:G. P. Scott, and G. A. Swarup. 6229: 6216: 6201: 6166: 6151: 6117:Swarup, G. Ananda (1977–1978). 6110: 6075: 6033: 5992: 5970: 5952: 5934: 3480:is a finite generating set for 1968:{\displaystyle e(F(X))=\infty } 1545:{\displaystyle e(\Gamma (G,S))} 1265:infinite connected components. 322:if for every finite collection 16:In the mathematical subject of 5893: 5873: 5837: 5828: 5819: 5810: 5797: 5779: 5747:Free product with amalgamation 5609:, such as for the case where 5525: 5513: 5437:is called a semi-splitting of 5418: 5406: 5339: 5327: 5294:of a finitely generated group 5056:as the fundamental group of a 4834: 4828: 4744: 4738: 4563: 4435:free product with amalgamation 4351: 4345: 4277: 4271: 4099: 4051: 4045: 3921:free product with amalgamation 3831: 3825: 3802: 3783: 3528: 3516: 3408:be finite generating sets for 3349: 3343: 3211: 3192: 3166: 3160: 3059: 3040: 2863: 2844: 2777: 2758: 2387: 2375: 2281:Cuts and almost invariant sets 2119: 2113: 2034: 2028: 1956: 1953: 1947: 1941: 1911: 1903: 1876: 1870: 1836: 1821: 1757: 1749: 1672: 1666: 1611: 1605: 1539: 1536: 1524: 1518: 1495: 1492: 1480: 1474: 1465: 1459: 1369: 1357: 1068: 1062: 875: 869: 826: 820: 771: 765: 736: 730: 701: 695: 640: 634: 565: 559: 530: 524: 463: 457: 428: 422: 303: 297: 1: 6238:An algebraic annulus theorem. 6018:10.1016/S0040-9383(99)00078-6 4988:. A finitely generated group 3776:. It is not hard to see that 2272:is either infinite cyclic or 6278:The algebraic torus theorem. 6187:10.1016/0022-4049(89)90014-5 6136:10.1016/0022-4049(77)90042-1 6096:10.1016/0022-4049(77)90051-2 5919:10.1016/0022-4049(83)90037-3 5902:"On accessibility of groups" 5496:{\displaystyle H\leqslant G} 5287:{\displaystyle H\leqslant G} 4846:{\displaystyle e(G)=\infty } 4457:is a finite group such that 3943:is a finite group such that 3704:consists of all elements of 2949:{\displaystyle A\subseteq G} 2585:{\displaystyle A\subseteq G} 2463:{\displaystyle A\subseteq G} 2328:{\displaystyle S\subseteq G} 2185:contains an infinite cyclic 1732:{\displaystyle \mathbb {Z} } 1375:{\displaystyle \Gamma (G,S)} 1316:{\displaystyle S\subseteq G} 1212:{\displaystyle F\subseteq K} 1146:{\displaystyle n\geqslant 0} 999:{\displaystyle F\subseteq K} 678:{\displaystyle n\geqslant 0} 577:{\displaystyle e(\Gamma )=m} 440:{\displaystyle e(\Gamma )=m} 260:{\displaystyle n\geqslant 0} 81:. In the modern language of 7: 5940:M. Bestvina and M. Feighn. 5740: 5537:{\displaystyle e(G,H)>1} 5430:{\displaystyle e(G,H)>1} 5316:the number of relative ends 5217:the hyperbolic boundary of 4035:are finitely generated and 2709:. Note that by definition 10: 6383: 1153:there exists a finite set 1087:, then for any finite set 940:there exists a finite set 900:, then for any finite set 832:{\displaystyle e(\Gamma )} 777:{\displaystyle e(\Gamma )} 151: 136:The theorem was proved by 5697:finitely presented groups 5643:finitely generated groups 5544:corresponds to the group 5266:finitely generated groups 5090:finitely generated groups 4756:{\displaystyle e(G)>1} 4426:{\displaystyle G=H*_{C}K} 4363:{\displaystyle e(G)>1} 4289:{\displaystyle e(G)>1} 4063:{\displaystyle e(G)>1} 3912:{\displaystyle G=H*_{C}K} 3843:{\displaystyle e(G)>1} 3808:{\displaystyle (A,A^{*})} 3473:{\displaystyle S=X\cup Y} 3361:{\displaystyle e(G)>1} 3307:finitely generated groups 3217:{\displaystyle (A,A^{*})} 3178:{\displaystyle e(G)>1} 3065:{\displaystyle (A,A^{*})} 2869:{\displaystyle (A,A^{*})} 2783:{\displaystyle (A,A^{*})} 2662:connecting a vertex from 1980:Freudenthal-Hopf theorems 1238:{\displaystyle \Gamma -K} 1025:{\displaystyle \Gamma -F} 381:{\displaystyle \Gamma -F} 6367:Theorems in group theory 6282:Inventiones Mathematicae 5965:Inventiones Mathematicae 5947:Inventiones Mathematicae 5868:Inventiones Mathematicae 5772: 5086:finitely presented group 4975:finitely generated group 4816:finitely generated group 4707:finitely generated group 4330:finitely generated group 4259:finitely generated group 3855:finitely generated group 2830:{\displaystyle \delta A} 2615:{\displaystyle \delta A} 2307:finitely generated group 2082:finitely generated group 1997:finitely generated group 1635:finitely generated group 1628:Basic facts and examples 1295:finitely generated group 71:amalgamated free product 26:finitely generated group 5900:Linnell, P. A. (1983). 4502:{\displaystyle C\neq K} 4476:{\displaystyle C\neq H} 3988:{\displaystyle C\neq K} 3962:{\displaystyle C\neq H} 2807:{\displaystyle \Gamma } 2655:{\displaystyle \Gamma } 1186:{\displaystyle \Gamma } 1120:{\displaystyle \Gamma } 973:{\displaystyle \Gamma } 933:{\displaystyle \Gamma } 852:{\displaystyle \Gamma } 800:{\displaystyle \Gamma } 355:{\displaystyle \Gamma } 280:{\displaystyle \Gamma } 223:{\displaystyle \Gamma } 195:{\displaystyle \Gamma } 171:{\displaystyle \Gamma } 6362:Geometric group theory 5767:Geometric group theory 5721: 5689: 5669: 5635:word-hyperbolic groups 5623: 5603: 5582: 5558: 5538: 5497: 5471: 5451: 5431: 5390: 5370: 5346: 5345:{\displaystyle e(G,H)} 5308: 5288: 5255: 5231: 5211: 5188: 5168: 5141: 5114: 5074: 5050: 5026: 5002: 4979:geometric group theory 4943: 4923: 4903: 4867: 4847: 4808: 4777: 4757: 4722: 4691: 4673:are isomorphic finite 4667: 4640: 4613: 4527: 4503: 4477: 4451: 4427: 4388: 4364: 4322: 4290: 4251: 4231: 4213:are isomorphic finite 4207: 4180: 4149: 4064: 4029: 4009: 3989: 3963: 3937: 3913: 3870: 3844: 3809: 3770: 3750: 3718: 3698: 3671: 3651: 3619: 3599: 3579: 3559: 3535: 3494: 3474: 3442: 3422: 3402: 3382: 3362: 3327: 3299: 3279: 3259: 3218: 3179: 3139:is almost invariant). 3133: 3113: 3086: 3066: 3027: 3004: 2980: 2979:{\displaystyle g\in G} 2950: 2921: 2894: 2870: 2831: 2808: 2784: 2742: 2703: 2676: 2656: 2636: 2616: 2586: 2557: 2537: 2517: 2491: 2464: 2438: 2418: 2394: 2353: 2329: 2299: 2266: 2238: 2218: 2179: 2152: 2132: 2131:{\displaystyle e(G)=2} 2097: 2071: 2012: 1969: 1925: 1883: 1849: 1805: 1770: 1733: 1705: 1685: 1684:{\displaystyle e(G)=0} 1650: 1618: 1589: 1569: 1546: 1502: 1443: 1420: 1400: 1376: 1341: 1317: 1287: 1259: 1239: 1213: 1187: 1167: 1147: 1121: 1101: 1081: 1046: 1026: 1000: 974: 954: 934: 914: 894: 853: 833: 801: 778: 749: 714: 679: 653: 618: 598: 578: 543: 508: 476: 441: 402: 382: 356: 336: 316: 281: 261: 224: 196: 172: 119: 99: 62: 41: 5881:An inaccessible group 5792:Annals of Mathematics 5722: 5690: 5670: 5624: 5604: 5583: 5559: 5539: 5498: 5472: 5452: 5432: 5391: 5371: 5347: 5309: 5289: 5256: 5239:topological dimension 5232: 5212: 5196:word-hyperbolic group 5189: 5169: 5142: 5115: 5075: 5051: 5027: 5003: 4944: 4924: 4904: 4902:{\displaystyle G=A*B} 4868: 4848: 4809: 4778: 4758: 4723: 4692: 4668: 4666:{\displaystyle C_{2}} 4641: 4639:{\displaystyle C_{1}} 4614: 4528: 4504: 4478: 4452: 4428: 4389: 4365: 4323: 4291: 4252: 4232: 4208: 4206:{\displaystyle C_{2}} 4181: 4179:{\displaystyle C_{1}} 4150: 4065: 4030: 4010: 3990: 3964: 3938: 3914: 3871: 3845: 3810: 3771: 3751: 3749:{\displaystyle G=H*K} 3719: 3699: 3697:{\displaystyle A^{*}} 3672: 3652: 3650:{\displaystyle G=H*K} 3620: 3600: 3580: 3560: 3536: 3495: 3475: 3443: 3423: 3403: 3383: 3363: 3328: 3300: 3280: 3260: 3258:{\displaystyle G=H*K} 3219: 3180: 3134: 3114: 3112:{\displaystyle A^{*}} 3087: 3067: 3028: 3005: 2981: 2951: 2922: 2920:{\displaystyle A^{*}} 2895: 2871: 2832: 2809: 2785: 2743: 2704: 2702:{\displaystyle A^{*}} 2677: 2657: 2637: 2617: 2587: 2558: 2538: 2518: 2492: 2490:{\displaystyle A^{*}} 2465: 2439: 2419: 2395: 2354: 2330: 2300: 2267: 2239: 2219: 2180: 2153: 2133: 2098: 2072: 2013: 1970: 1926: 1884: 1850: 1806: 1771: 1734: 1716:infinite cyclic group 1706: 1686: 1651: 1619: 1590: 1570: 1547: 1503: 1444: 1421: 1401: 1377: 1342: 1318: 1288: 1260: 1240: 1214: 1188: 1168: 1148: 1122: 1102: 1082: 1047: 1027: 1001: 975: 955: 935: 915: 895: 854: 834: 802: 786:the number of ends of 779: 750: 715: 680: 654: 619: 599: 579: 544: 509: 477: 442: 403: 383: 357: 337: 317: 282: 262: 225: 197: 173: 120: 100: 63: 42: 5711: 5679: 5659: 5613: 5593: 5572: 5548: 5507: 5481: 5461: 5441: 5400: 5380: 5360: 5354:Schreier coset graph 5321: 5298: 5272: 5245: 5241:zero if and only if 5221: 5201: 5178: 5158: 5131: 5104: 5064: 5040: 5016: 4992: 4986:accessibility theory 4933: 4913: 4881: 4857: 4822: 4798: 4767: 4732: 4712: 4681: 4650: 4623: 4541: 4517: 4487: 4461: 4441: 4398: 4378: 4339: 4312: 4265: 4241: 4221: 4190: 4163: 4077: 4039: 4019: 3999: 3973: 3947: 3927: 3884: 3860: 3819: 3780: 3760: 3728: 3708: 3681: 3661: 3629: 3609: 3589: 3569: 3549: 3504: 3484: 3452: 3448:accordingly so that 3432: 3412: 3392: 3372: 3337: 3317: 3289: 3269: 3237: 3189: 3154: 3123: 3096: 3076: 3037: 3014: 2994: 2988:symmetric difference 2964: 2934: 2904: 2884: 2841: 2818: 2798: 2755: 2713: 2686: 2666: 2646: 2626: 2603: 2570: 2547: 2527: 2501: 2474: 2448: 2428: 2408: 2363: 2343: 2313: 2289: 2248: 2228: 2208: 2169: 2142: 2107: 2087: 2022: 2002: 1935: 1893: 1882:{\displaystyle F(X)} 1864: 1815: 1786: 1743: 1721: 1695: 1660: 1640: 1617:{\displaystyle e(G)} 1599: 1579: 1559: 1512: 1453: 1433: 1410: 1390: 1351: 1331: 1301: 1277: 1249: 1223: 1197: 1177: 1157: 1131: 1127:and for any integer 1111: 1091: 1056: 1036: 1010: 984: 964: 944: 924: 904: 863: 843: 814: 791: 759: 724: 689: 663: 628: 608: 588: 553: 518: 486: 451: 416: 410:connected components 392: 366: 346: 326: 291: 271: 245: 214: 210:. Then the ends of 186: 162: 109: 89: 52: 31: 6315:Geometriae Dedicata 5843:John R. Stallings. 5785:John R. Stallings. 5701:Riemannian geometry 4794:For the case where 4701:In the language of 4394:admits a splitting 2682:with a vertex from 2516:{\displaystyle G-A} 2265:{\displaystyle G/W} 287:is said to satisfy 6296:Cutting up graphs. 6244:2007-07-15 at the 5985:2011-06-05 at the 5717: 5685: 5665: 5619: 5599: 5578: 5554: 5534: 5493: 5467: 5447: 5427: 5396:. The case where 5386: 5366: 5342: 5304: 5284: 5261:is virtually free. 5251: 5227: 5207: 5184: 5164: 5137: 5110: 5084:proved that every 5070: 5046: 5022: 4998: 4939: 4919: 4899: 4863: 4843: 4814:is a torsion-free 4804: 4773: 4753: 4718: 4687: 4663: 4636: 4609: 4523: 4499: 4473: 4447: 4423: 4384: 4360: 4318: 4286: 4247: 4227: 4203: 4176: 4145: 4060: 4025: 4005: 3985: 3959: 3933: 3909: 3866: 3840: 3805: 3766: 3746: 3714: 3694: 3667: 3647: 3615: 3595: 3575: 3555: 3531: 3490: 3470: 3438: 3418: 3398: 3378: 3358: 3323: 3295: 3275: 3255: 3214: 3175: 3129: 3109: 3082: 3062: 3026:{\displaystyle Ag} 3023: 3000: 2976: 2946: 2917: 2890: 2866: 2827: 2804: 2780: 2738: 2699: 2672: 2652: 2632: 2612: 2582: 2553: 2533: 2513: 2487: 2460: 2434: 2414: 2390: 2349: 2325: 2295: 2262: 2234: 2214: 2198:Charles T. C. Wall 2175: 2148: 2128: 2093: 2067: 2008: 1987:and independently 1965: 1921: 1879: 1845: 1801: 1780:free abelian group 1766: 1729: 1701: 1681: 1646: 1614: 1585: 1565: 1542: 1498: 1439: 1416: 1396: 1372: 1337: 1313: 1283: 1255: 1235: 1209: 1183: 1163: 1143: 1117: 1097: 1077: 1042: 1022: 996: 970: 950: 930: 910: 890: 849: 829: 797: 774: 745: 710: 675: 649: 614: 594: 574: 539: 504: 472: 437: 398: 378: 352: 332: 312: 277: 257: 220: 192: 168: 154:End (graph theory) 115: 95: 58: 37: 6308:Graham A. Niblo. 6222:V. N. Gerasimov. 5757:Bass–Serre theory 5720:{\displaystyle 4} 5688:{\displaystyle G} 5668:{\displaystyle H} 5622:{\displaystyle H} 5602:{\displaystyle H} 5581:{\displaystyle H} 5557:{\displaystyle G} 5470:{\displaystyle H} 5450:{\displaystyle G} 5389:{\displaystyle H} 5369:{\displaystyle G} 5307:{\displaystyle G} 5254:{\displaystyle G} 5230:{\displaystyle G} 5210:{\displaystyle G} 5187:{\displaystyle G} 5167:{\displaystyle G} 5140:{\displaystyle G} 5113:{\displaystyle G} 5073:{\displaystyle G} 5049:{\displaystyle G} 5034:Bass–Serre theory 5025:{\displaystyle G} 5001:{\displaystyle G} 4942:{\displaystyle B} 4922:{\displaystyle A} 4866:{\displaystyle G} 4807:{\displaystyle G} 4776:{\displaystyle G} 4721:{\displaystyle G} 4703:Bass–Serre theory 4690:{\displaystyle H} 4526:{\displaystyle G} 4450:{\displaystyle C} 4387:{\displaystyle G} 4321:{\displaystyle G} 4250:{\displaystyle G} 4230:{\displaystyle H} 4028:{\displaystyle K} 4008:{\displaystyle H} 3936:{\displaystyle C} 3869:{\displaystyle G} 3769:{\displaystyle K} 3717:{\displaystyle G} 3670:{\displaystyle H} 3618:{\displaystyle G} 3598:{\displaystyle A} 3578:{\displaystyle S} 3558:{\displaystyle G} 3493:{\displaystyle G} 3441:{\displaystyle K} 3421:{\displaystyle H} 3401:{\displaystyle Y} 3381:{\displaystyle X} 3326:{\displaystyle G} 3298:{\displaystyle K} 3278:{\displaystyle H} 3132:{\displaystyle A} 3085:{\displaystyle A} 3003:{\displaystyle A} 2893:{\displaystyle A} 2880:if both the sets 2837:is finite. A cut 2675:{\displaystyle A} 2635:{\displaystyle A} 2556:{\displaystyle G} 2536:{\displaystyle A} 2437:{\displaystyle S} 2417:{\displaystyle G} 2352:{\displaystyle G} 2298:{\displaystyle G} 2274:infinite dihedral 2237:{\displaystyle W} 2217:{\displaystyle G} 2178:{\displaystyle G} 2151:{\displaystyle G} 2096:{\displaystyle G} 2011:{\displaystyle G} 1704:{\displaystyle G} 1649:{\displaystyle G} 1624:is well-defined. 1588:{\displaystyle G} 1568:{\displaystyle S} 1442:{\displaystyle G} 1428:number of ends of 1419:{\displaystyle S} 1399:{\displaystyle G} 1340:{\displaystyle G} 1286:{\displaystyle G} 1258:{\displaystyle n} 1166:{\displaystyle K} 1100:{\displaystyle F} 1045:{\displaystyle m} 953:{\displaystyle K} 913:{\displaystyle F} 617:{\displaystyle n} 597:{\displaystyle m} 482:and if for every 412:. By definition, 401:{\displaystyle n} 335:{\displaystyle F} 204:topological space 138:John R. Stallings 118:{\displaystyle G} 98:{\displaystyle G} 83:Bass–Serre theory 61:{\displaystyle G} 40:{\displaystyle G} 6374: 6346: 6337: 6331: 6324: 6318: 6306: 6300: 6293:M. J. Dunwoody. 6291: 6285: 6273: 6267: 6264:Acta Mathematica 6257:B. H. Bowditch. 6255: 6249: 6233: 6227: 6220: 6214: 6205: 6199: 6198: 6170: 6164: 6155: 6149: 6148: 6138: 6114: 6108: 6107: 6090:(1–3): 179–198. 6079: 6073: 6070: 6061: 6055: 6046: 6037: 6031: 6030: 6020: 5996: 5990: 5974: 5968: 5956: 5950: 5938: 5932: 5931: 5921: 5897: 5891: 5879:M. J. Dunwoody. 5877: 5871: 5861:M. J. Dunwoody. 5859: 5850: 5841: 5835: 5832: 5826: 5823: 5817: 5814: 5808: 5803:John Stallings. 5801: 5795: 5783: 5726: 5724: 5723: 5718: 5705:minimal surfaces 5694: 5692: 5691: 5686: 5674: 5672: 5671: 5666: 5628: 5626: 5625: 5620: 5608: 5606: 5605: 5600: 5587: 5585: 5584: 5579: 5563: 5561: 5560: 5555: 5543: 5541: 5540: 5535: 5502: 5500: 5499: 5494: 5476: 5474: 5473: 5468: 5456: 5454: 5453: 5448: 5436: 5434: 5433: 5428: 5395: 5393: 5392: 5387: 5376:with respect to 5375: 5373: 5372: 5367: 5351: 5349: 5348: 5343: 5313: 5311: 5310: 5305: 5293: 5291: 5290: 5285: 5260: 5258: 5257: 5252: 5236: 5234: 5233: 5228: 5216: 5214: 5213: 5208: 5193: 5191: 5190: 5185: 5173: 5171: 5170: 5165: 5146: 5144: 5143: 5138: 5119: 5117: 5116: 5111: 5079: 5077: 5076: 5071: 5055: 5053: 5052: 5047: 5031: 5029: 5028: 5023: 5007: 5005: 5004: 4999: 4948: 4946: 4945: 4940: 4928: 4926: 4925: 4920: 4908: 4906: 4905: 4900: 4873:admits a proper 4872: 4870: 4869: 4864: 4852: 4850: 4849: 4844: 4813: 4811: 4810: 4805: 4787:on a simplicial 4782: 4780: 4779: 4774: 4762: 4760: 4759: 4754: 4727: 4725: 4724: 4719: 4696: 4694: 4693: 4688: 4672: 4670: 4669: 4664: 4662: 4661: 4645: 4643: 4642: 4637: 4635: 4634: 4618: 4616: 4615: 4610: 4605: 4604: 4589: 4588: 4579: 4578: 4566: 4532: 4530: 4529: 4524: 4508: 4506: 4505: 4500: 4482: 4480: 4479: 4474: 4456: 4454: 4453: 4448: 4432: 4430: 4429: 4424: 4419: 4418: 4393: 4391: 4390: 4385: 4369: 4367: 4366: 4361: 4327: 4325: 4324: 4319: 4295: 4293: 4292: 4287: 4256: 4254: 4253: 4248: 4236: 4234: 4233: 4228: 4212: 4210: 4209: 4204: 4202: 4201: 4185: 4183: 4182: 4177: 4175: 4174: 4154: 4152: 4151: 4146: 4141: 4140: 4125: 4124: 4115: 4114: 4102: 4069: 4067: 4066: 4061: 4034: 4032: 4031: 4026: 4014: 4012: 4011: 4006: 3994: 3992: 3991: 3986: 3968: 3966: 3965: 3960: 3942: 3940: 3939: 3934: 3918: 3916: 3915: 3910: 3905: 3904: 3875: 3873: 3872: 3867: 3849: 3847: 3846: 3841: 3814: 3812: 3811: 3806: 3801: 3800: 3775: 3773: 3772: 3767: 3755: 3753: 3752: 3747: 3723: 3721: 3720: 3715: 3703: 3701: 3700: 3695: 3693: 3692: 3676: 3674: 3673: 3668: 3656: 3654: 3653: 3648: 3624: 3622: 3621: 3616: 3604: 3602: 3601: 3596: 3584: 3582: 3581: 3576: 3565:with respect to 3564: 3562: 3561: 3556: 3540: 3538: 3537: 3532: 3499: 3497: 3496: 3491: 3479: 3477: 3476: 3471: 3447: 3445: 3444: 3439: 3427: 3425: 3424: 3419: 3407: 3405: 3404: 3399: 3387: 3385: 3384: 3379: 3367: 3365: 3364: 3359: 3332: 3330: 3329: 3324: 3304: 3302: 3301: 3296: 3284: 3282: 3281: 3276: 3264: 3262: 3261: 3256: 3223: 3221: 3220: 3215: 3210: 3209: 3184: 3182: 3181: 3176: 3138: 3136: 3135: 3130: 3118: 3116: 3115: 3110: 3108: 3107: 3091: 3089: 3088: 3083: 3071: 3069: 3068: 3063: 3058: 3057: 3032: 3030: 3029: 3024: 3009: 3007: 3006: 3001: 2985: 2983: 2982: 2977: 2958:almost invariant 2955: 2953: 2952: 2947: 2926: 2924: 2923: 2918: 2916: 2915: 2899: 2897: 2896: 2891: 2875: 2873: 2872: 2867: 2862: 2861: 2836: 2834: 2833: 2828: 2813: 2811: 2810: 2805: 2789: 2787: 2786: 2781: 2776: 2775: 2751:An ordered pair 2747: 2745: 2744: 2739: 2737: 2736: 2708: 2706: 2705: 2700: 2698: 2697: 2681: 2679: 2678: 2673: 2661: 2659: 2658: 2653: 2641: 2639: 2638: 2633: 2621: 2619: 2618: 2613: 2591: 2589: 2588: 2583: 2562: 2560: 2559: 2554: 2542: 2540: 2539: 2534: 2522: 2520: 2519: 2514: 2496: 2494: 2493: 2488: 2486: 2485: 2469: 2467: 2466: 2461: 2443: 2441: 2440: 2435: 2424:with respect to 2423: 2421: 2420: 2415: 2399: 2397: 2396: 2391: 2358: 2356: 2355: 2350: 2334: 2332: 2331: 2326: 2304: 2302: 2301: 2296: 2271: 2269: 2268: 2263: 2258: 2243: 2241: 2240: 2235: 2223: 2221: 2220: 2215: 2184: 2182: 2181: 2176: 2157: 2155: 2154: 2149: 2137: 2135: 2134: 2129: 2102: 2100: 2099: 2094: 2076: 2074: 2073: 2068: 2017: 2015: 2014: 2009: 1985:Hans Freudenthal 1974: 1972: 1971: 1966: 1930: 1928: 1927: 1922: 1914: 1906: 1888: 1886: 1885: 1880: 1854: 1852: 1851: 1846: 1835: 1834: 1829: 1810: 1808: 1807: 1802: 1800: 1799: 1794: 1775: 1773: 1772: 1767: 1756: 1738: 1736: 1735: 1730: 1728: 1710: 1708: 1707: 1702: 1690: 1688: 1687: 1682: 1655: 1653: 1652: 1647: 1623: 1621: 1620: 1615: 1594: 1592: 1591: 1586: 1574: 1572: 1571: 1566: 1551: 1549: 1548: 1543: 1507: 1505: 1504: 1499: 1448: 1446: 1445: 1440: 1425: 1423: 1422: 1417: 1406:with respect to 1405: 1403: 1402: 1397: 1381: 1379: 1378: 1373: 1346: 1344: 1343: 1338: 1322: 1320: 1319: 1314: 1292: 1290: 1289: 1284: 1264: 1262: 1261: 1256: 1244: 1242: 1241: 1236: 1218: 1216: 1215: 1210: 1192: 1190: 1189: 1184: 1172: 1170: 1169: 1164: 1152: 1150: 1149: 1144: 1126: 1124: 1123: 1118: 1106: 1104: 1103: 1098: 1086: 1084: 1083: 1078: 1051: 1049: 1048: 1043: 1031: 1029: 1028: 1023: 1005: 1003: 1002: 997: 979: 977: 976: 971: 959: 957: 956: 951: 939: 937: 936: 931: 919: 917: 916: 911: 899: 897: 896: 891: 858: 856: 855: 850: 838: 836: 835: 830: 806: 804: 803: 798: 783: 781: 780: 775: 754: 752: 751: 746: 719: 717: 716: 711: 684: 682: 681: 676: 658: 656: 655: 650: 623: 621: 620: 615: 603: 601: 600: 595: 583: 581: 580: 575: 548: 546: 545: 540: 513: 511: 510: 505: 481: 479: 478: 473: 446: 444: 443: 438: 407: 405: 404: 399: 387: 385: 384: 379: 361: 359: 358: 353: 341: 339: 338: 333: 321: 319: 318: 313: 286: 284: 283: 278: 266: 264: 263: 258: 229: 227: 226: 221: 201: 199: 198: 193: 177: 175: 174: 169: 129:on a simplicial 124: 122: 121: 116: 104: 102: 101: 96: 67: 65: 64: 59: 46: 44: 43: 38: 6382: 6381: 6377: 6376: 6375: 6373: 6372: 6371: 6352: 6351: 6350: 6349: 6338: 6334: 6326:C. T. C. Wall. 6325: 6321: 6307: 6303: 6292: 6288: 6274: 6270: 6256: 6252: 6246:Wayback Machine 6234: 6230: 6221: 6217: 6207:Michah Sageev. 6206: 6202: 6171: 6167: 6156: 6152: 6115: 6111: 6080: 6076: 6071: 6064: 6056: 6049: 6038: 6034: 5997: 5993: 5987:Wayback Machine 5975: 5971: 5957: 5953: 5939: 5935: 5898: 5894: 5878: 5874: 5860: 5853: 5842: 5838: 5833: 5829: 5824: 5820: 5815: 5811: 5802: 5798: 5784: 5780: 5775: 5762:Graph of groups 5743: 5712: 5709: 5708: 5680: 5677: 5676: 5660: 5657: 5656: 5614: 5611: 5610: 5594: 5591: 5590: 5573: 5570: 5569: 5549: 5546: 5545: 5508: 5505: 5504: 5482: 5479: 5478: 5462: 5459: 5458: 5442: 5439: 5438: 5401: 5398: 5397: 5381: 5378: 5377: 5361: 5358: 5357: 5322: 5319: 5318: 5299: 5296: 5295: 5273: 5270: 5269: 5246: 5243: 5242: 5222: 5219: 5218: 5202: 5199: 5198: 5179: 5176: 5175: 5159: 5156: 5155: 5149:graph of groups 5132: 5129: 5128: 5127:if and only if 5105: 5102: 5101: 5065: 5062: 5061: 5058:graph of groups 5041: 5038: 5037: 5017: 5014: 5013: 4993: 4990: 4989: 4973:invariant of a 4955: 4934: 4931: 4930: 4914: 4911: 4910: 4882: 4879: 4878: 4858: 4855: 4854: 4853:if and only if 4823: 4820: 4819: 4799: 4796: 4795: 4768: 4765: 4764: 4763:if and only if 4733: 4730: 4729: 4713: 4710: 4709: 4682: 4679: 4678: 4657: 4653: 4651: 4648: 4647: 4630: 4626: 4624: 4621: 4620: 4600: 4596: 4584: 4580: 4571: 4567: 4562: 4542: 4539: 4538: 4518: 4515: 4514: 4488: 4485: 4484: 4462: 4459: 4458: 4442: 4439: 4438: 4414: 4410: 4399: 4396: 4395: 4379: 4376: 4375: 4340: 4337: 4336: 4313: 4310: 4309: 4306: 4266: 4263: 4262: 4242: 4239: 4238: 4222: 4219: 4218: 4197: 4193: 4191: 4188: 4187: 4170: 4166: 4164: 4161: 4160: 4136: 4132: 4120: 4116: 4107: 4103: 4098: 4078: 4075: 4074: 4040: 4037: 4036: 4020: 4017: 4016: 4000: 3997: 3996: 3974: 3971: 3970: 3948: 3945: 3944: 3928: 3925: 3924: 3900: 3896: 3885: 3882: 3881: 3861: 3858: 3857: 3820: 3817: 3816: 3796: 3792: 3781: 3778: 3777: 3761: 3758: 3757: 3729: 3726: 3725: 3709: 3706: 3705: 3688: 3684: 3682: 3679: 3678: 3662: 3659: 3658: 3630: 3627: 3626: 3610: 3607: 3606: 3590: 3587: 3586: 3570: 3567: 3566: 3550: 3547: 3546: 3505: 3502: 3501: 3485: 3482: 3481: 3453: 3450: 3449: 3433: 3430: 3429: 3413: 3410: 3409: 3393: 3390: 3389: 3373: 3370: 3369: 3338: 3335: 3334: 3318: 3315: 3314: 3305:are nontrivial 3290: 3287: 3286: 3270: 3267: 3266: 3238: 3235: 3234: 3231: 3205: 3201: 3190: 3187: 3186: 3155: 3152: 3151: 3145: 3124: 3121: 3120: 3103: 3099: 3097: 3094: 3093: 3077: 3074: 3073: 3053: 3049: 3038: 3035: 3034: 3015: 3012: 3011: 2995: 2992: 2991: 2965: 2962: 2961: 2935: 2932: 2931: 2911: 2907: 2905: 2902: 2901: 2885: 2882: 2881: 2857: 2853: 2842: 2839: 2838: 2819: 2816: 2815: 2799: 2796: 2795: 2771: 2767: 2756: 2753: 2752: 2732: 2728: 2714: 2711: 2710: 2693: 2689: 2687: 2684: 2683: 2667: 2664: 2663: 2647: 2644: 2643: 2627: 2624: 2623: 2604: 2601: 2600: 2571: 2568: 2567: 2548: 2545: 2544: 2528: 2525: 2524: 2502: 2499: 2498: 2497:the complement 2481: 2477: 2475: 2472: 2471: 2449: 2446: 2445: 2444:. For a subset 2429: 2426: 2425: 2409: 2406: 2405: 2364: 2361: 2360: 2344: 2341: 2340: 2314: 2311: 2310: 2290: 2287: 2286: 2283: 2254: 2249: 2246: 2245: 2229: 2226: 2225: 2209: 2206: 2205: 2170: 2167: 2166: 2163:infinite cyclic 2143: 2140: 2139: 2138:if and only if 2108: 2105: 2104: 2088: 2085: 2084: 2023: 2020: 2019: 2003: 2000: 1999: 1982: 1936: 1933: 1932: 1910: 1902: 1894: 1891: 1890: 1865: 1862: 1861: 1830: 1825: 1824: 1816: 1813: 1812: 1795: 1790: 1789: 1787: 1784: 1783: 1752: 1744: 1741: 1740: 1724: 1722: 1719: 1718: 1696: 1693: 1692: 1691:if and only if 1661: 1658: 1657: 1641: 1638: 1637: 1630: 1600: 1597: 1596: 1580: 1577: 1576: 1560: 1557: 1556: 1513: 1510: 1509: 1454: 1451: 1450: 1434: 1431: 1430: 1411: 1408: 1407: 1391: 1388: 1387: 1352: 1349: 1348: 1332: 1329: 1328: 1302: 1299: 1298: 1278: 1275: 1274: 1271: 1250: 1247: 1246: 1224: 1221: 1220: 1198: 1195: 1194: 1178: 1175: 1174: 1158: 1155: 1154: 1132: 1129: 1128: 1112: 1109: 1108: 1092: 1089: 1088: 1057: 1054: 1053: 1037: 1034: 1033: 1011: 1008: 1007: 985: 982: 981: 965: 962: 961: 945: 942: 941: 925: 922: 921: 905: 902: 901: 864: 861: 860: 844: 841: 840: 815: 812: 811: 792: 789: 788: 760: 757: 756: 725: 722: 721: 690: 687: 686: 664: 661: 660: 629: 626: 625: 609: 606: 605: 589: 586: 585: 554: 551: 550: 549:is false. Thus 519: 516: 515: 487: 484: 483: 452: 449: 448: 417: 414: 413: 393: 390: 389: 367: 364: 363: 347: 344: 343: 327: 324: 323: 292: 289: 288: 272: 269: 268: 246: 243: 242: 236:ends of a graph 215: 212: 211: 187: 184: 183: 178:be a connected 163: 160: 159: 156: 150: 140:, first in the 110: 107: 106: 90: 87: 86: 53: 50: 49: 32: 29: 28: 12: 11: 5: 6380: 6370: 6369: 6364: 6348: 6347: 6332: 6319: 6301: 6286: 6268: 6250: 6228: 6215: 6200: 6181:(2): 197–210. 6165: 6150: 6129:(1–3): 75–82. 6109: 6074: 6062: 6047: 6032: 6011:(3): 617–629. 5991: 5969: 5951: 5933: 5892: 5872: 5851: 5836: 5827: 5818: 5809: 5796: 5777: 5776: 5774: 5771: 5770: 5769: 5764: 5759: 5754: 5749: 5742: 5739: 5738: 5737: 5716: 5703:techniques of 5684: 5664: 5647: 5646: 5618: 5598: 5577: 5553: 5533: 5530: 5527: 5524: 5521: 5518: 5515: 5512: 5503:the condition 5492: 5489: 5486: 5466: 5446: 5426: 5423: 5420: 5417: 5414: 5411: 5408: 5405: 5385: 5365: 5341: 5338: 5335: 5332: 5329: 5326: 5303: 5283: 5280: 5277: 5262: 5250: 5226: 5206: 5183: 5163: 5152: 5136: 5109: 5098: 5069: 5045: 5021: 5008:is said to be 4997: 4982: 4971:quasi-isometry 4967: 4954: 4951: 4938: 4918: 4898: 4895: 4892: 4889: 4886: 4877:decomposition 4862: 4842: 4839: 4836: 4833: 4830: 4827: 4803: 4772: 4752: 4749: 4746: 4743: 4740: 4737: 4717: 4699: 4698: 4686: 4660: 4656: 4633: 4629: 4608: 4603: 4599: 4595: 4592: 4587: 4583: 4577: 4574: 4570: 4565: 4561: 4558: 4555: 4552: 4549: 4546: 4522: 4510: 4498: 4495: 4492: 4472: 4469: 4466: 4446: 4422: 4417: 4413: 4409: 4406: 4403: 4383: 4359: 4356: 4353: 4350: 4347: 4344: 4317: 4305: 4302: 4298: 4297: 4285: 4282: 4279: 4276: 4273: 4270: 4246: 4226: 4200: 4196: 4173: 4169: 4144: 4139: 4135: 4131: 4128: 4123: 4119: 4113: 4110: 4106: 4101: 4097: 4094: 4091: 4088: 4085: 4082: 4071: 4059: 4056: 4053: 4050: 4047: 4044: 4024: 4004: 3984: 3981: 3978: 3958: 3955: 3952: 3932: 3908: 3903: 3899: 3895: 3892: 3889: 3865: 3839: 3836: 3833: 3830: 3827: 3824: 3804: 3799: 3795: 3791: 3788: 3785: 3765: 3745: 3742: 3739: 3736: 3733: 3713: 3691: 3687: 3666: 3646: 3643: 3640: 3637: 3634: 3614: 3594: 3574: 3554: 3530: 3527: 3524: 3521: 3518: 3515: 3512: 3509: 3489: 3469: 3466: 3463: 3460: 3457: 3437: 3417: 3397: 3377: 3368:. Indeed, let 3357: 3354: 3351: 3348: 3345: 3342: 3322: 3294: 3274: 3254: 3251: 3248: 3245: 3242: 3230: 3227: 3226: 3225: 3213: 3208: 3204: 3200: 3197: 3194: 3174: 3171: 3168: 3165: 3162: 3159: 3144: 3141: 3128: 3106: 3102: 3081: 3061: 3056: 3052: 3048: 3045: 3042: 3022: 3019: 2999: 2975: 2972: 2969: 2945: 2942: 2939: 2927:are infinite. 2914: 2910: 2889: 2865: 2860: 2856: 2852: 2849: 2846: 2826: 2823: 2803: 2779: 2774: 2770: 2766: 2763: 2760: 2735: 2731: 2727: 2724: 2721: 2718: 2696: 2692: 2671: 2651: 2631: 2611: 2608: 2581: 2578: 2575: 2552: 2532: 2512: 2509: 2506: 2484: 2480: 2459: 2456: 2453: 2433: 2413: 2389: 2386: 2383: 2380: 2377: 2374: 2371: 2368: 2348: 2337:generating set 2324: 2321: 2318: 2294: 2282: 2279: 2278: 2277: 2261: 2257: 2253: 2233: 2213: 2195: 2194: 2174: 2147: 2127: 2124: 2121: 2118: 2115: 2112: 2092: 2078: 2066: 2063: 2060: 2057: 2054: 2051: 2048: 2045: 2042: 2039: 2036: 2033: 2030: 2027: 2007: 1981: 1978: 1977: 1976: 1964: 1961: 1958: 1955: 1952: 1949: 1946: 1943: 1940: 1920: 1917: 1913: 1909: 1905: 1901: 1898: 1878: 1875: 1872: 1869: 1855: 1844: 1841: 1838: 1833: 1828: 1823: 1820: 1798: 1793: 1776: 1765: 1762: 1759: 1755: 1751: 1748: 1727: 1712: 1700: 1680: 1677: 1674: 1671: 1668: 1665: 1645: 1629: 1626: 1613: 1610: 1607: 1604: 1584: 1564: 1554:generating set 1541: 1538: 1535: 1532: 1529: 1526: 1523: 1520: 1517: 1497: 1494: 1491: 1488: 1485: 1482: 1479: 1476: 1473: 1470: 1467: 1464: 1461: 1458: 1449:is defined as 1438: 1415: 1395: 1371: 1368: 1365: 1362: 1359: 1356: 1336: 1325:generating set 1312: 1309: 1306: 1282: 1270: 1269:Ends of groups 1267: 1254: 1234: 1231: 1228: 1208: 1205: 1202: 1182: 1162: 1142: 1139: 1136: 1116: 1096: 1076: 1073: 1070: 1067: 1064: 1061: 1041: 1021: 1018: 1015: 995: 992: 989: 969: 949: 929: 909: 889: 886: 883: 880: 877: 874: 871: 868: 848: 828: 825: 822: 819: 796: 773: 770: 767: 764: 744: 741: 738: 735: 732: 729: 709: 706: 703: 700: 697: 694: 674: 671: 668: 648: 645: 642: 639: 636: 633: 613: 593: 573: 570: 567: 564: 561: 558: 538: 535: 532: 529: 526: 523: 514:the statement 503: 500: 497: 494: 491: 471: 468: 465: 462: 459: 456: 436: 433: 430: 427: 424: 421: 397: 377: 374: 371: 351: 331: 311: 308: 305: 302: 299: 296: 276: 256: 253: 250: 219: 191: 167: 152:Main article: 149: 148:Ends of graphs 146: 114: 94: 77:over a finite 57: 36: 24:states that a 9: 6: 4: 3: 2: 6379: 6368: 6365: 6363: 6360: 6359: 6357: 6344: 6343: 6339:M. Kapovich. 6336: 6329: 6323: 6316: 6313: 6312: 6305: 6298: 6297: 6290: 6283: 6280: 6279: 6272: 6265: 6262: 6261: 6254: 6247: 6243: 6240: 6239: 6232: 6225: 6219: 6212: 6211: 6204: 6196: 6192: 6188: 6184: 6180: 6176: 6169: 6162: 6161: 6154: 6146: 6142: 6137: 6132: 6128: 6124: 6120: 6113: 6105: 6101: 6097: 6093: 6089: 6085: 6078: 6069: 6067: 6060: 6054: 6052: 6044: 6043: 6036: 6028: 6024: 6019: 6014: 6010: 6006: 6002: 5995: 5988: 5984: 5981: 5980: 5973: 5966: 5963: 5962: 5955: 5948: 5945: 5944: 5937: 5929: 5925: 5920: 5915: 5911: 5907: 5903: 5896: 5890: 5889:0-521-43529-3 5886: 5882: 5876: 5869: 5866: 5865: 5858: 5856: 5848: 5847: 5840: 5831: 5822: 5813: 5806: 5800: 5793: 5790: 5789: 5782: 5778: 5768: 5765: 5763: 5760: 5758: 5755: 5753: 5752:HNN extension 5750: 5748: 5745: 5744: 5734: 5730: 5714: 5706: 5702: 5698: 5682: 5662: 5653: 5649: 5648: 5644: 5640: 5636: 5632: 5616: 5596: 5575: 5567: 5566:CAT(0)-cubing 5551: 5531: 5528: 5522: 5519: 5516: 5510: 5490: 5487: 5484: 5464: 5444: 5424: 5421: 5415: 5412: 5409: 5403: 5383: 5363: 5355: 5336: 5333: 5330: 5324: 5317: 5301: 5281: 5278: 5275: 5267: 5263: 5248: 5240: 5224: 5204: 5197: 5181: 5161: 5153: 5150: 5134: 5126: 5123: 5107: 5099: 5096: 5091: 5087: 5083: 5067: 5059: 5043: 5035: 5019: 5011: 4995: 4987: 4983: 4980: 4976: 4972: 4968: 4965: 4962: 4957: 4956: 4950: 4936: 4916: 4896: 4893: 4890: 4887: 4884: 4876: 4860: 4837: 4831: 4825: 4817: 4801: 4792: 4790: 4786: 4770: 4750: 4747: 4741: 4735: 4715: 4708: 4704: 4684: 4676: 4658: 4654: 4631: 4627: 4601: 4597: 4593: 4590: 4585: 4581: 4575: 4572: 4568: 4559: 4556: 4553: 4547: 4544: 4537: 4536:HNN extension 4533: 4520: 4511: 4496: 4493: 4490: 4470: 4467: 4464: 4444: 4436: 4420: 4415: 4411: 4407: 4404: 4401: 4381: 4373: 4372: 4371: 4357: 4354: 4348: 4342: 4333: 4331: 4315: 4301: 4283: 4280: 4274: 4268: 4260: 4244: 4224: 4216: 4198: 4194: 4171: 4167: 4158: 4157:HNN-extension 4137: 4133: 4129: 4126: 4121: 4117: 4111: 4108: 4104: 4095: 4092: 4089: 4083: 4080: 4072: 4057: 4054: 4048: 4042: 4022: 4002: 3982: 3979: 3976: 3956: 3953: 3950: 3930: 3922: 3906: 3901: 3897: 3893: 3890: 3887: 3879: 3878: 3877: 3863: 3856: 3851: 3837: 3834: 3828: 3822: 3797: 3793: 3789: 3786: 3763: 3743: 3740: 3737: 3734: 3731: 3711: 3689: 3685: 3664: 3644: 3641: 3638: 3635: 3632: 3612: 3592: 3572: 3552: 3544: 3525: 3522: 3519: 3510: 3487: 3467: 3464: 3461: 3458: 3455: 3435: 3415: 3395: 3375: 3355: 3352: 3346: 3340: 3320: 3312: 3308: 3292: 3272: 3252: 3249: 3246: 3243: 3240: 3206: 3202: 3198: 3195: 3172: 3169: 3163: 3157: 3150: 3149: 3148: 3143:Cuts and ends 3140: 3126: 3104: 3100: 3079: 3054: 3050: 3046: 3043: 3020: 3017: 2997: 2989: 2973: 2970: 2967: 2960:if for every 2959: 2943: 2940: 2937: 2928: 2912: 2908: 2887: 2879: 2858: 2854: 2850: 2847: 2824: 2821: 2793: 2772: 2768: 2764: 2761: 2749: 2733: 2729: 2725: 2722: 2719: 2716: 2694: 2690: 2669: 2629: 2609: 2606: 2599: 2595: 2594:edge boundary 2579: 2576: 2573: 2566:For a subset 2564: 2550: 2530: 2510: 2507: 2504: 2482: 2478: 2457: 2454: 2451: 2431: 2411: 2403: 2384: 2381: 2378: 2369: 2346: 2338: 2322: 2319: 2316: 2308: 2292: 2275: 2259: 2255: 2251: 2231: 2211: 2203: 2202: 2201: 2199: 2192: 2188: 2172: 2164: 2161: 2145: 2125: 2122: 2116: 2110: 2090: 2083: 2079: 2058: 2055: 2052: 2049: 2046: 2043: 2037: 2031: 2025: 2005: 1998: 1994: 1993: 1992: 1990: 1986: 1959: 1950: 1944: 1938: 1915: 1907: 1899: 1896: 1873: 1867: 1860: 1856: 1842: 1839: 1831: 1818: 1796: 1781: 1777: 1763: 1760: 1746: 1717: 1713: 1698: 1678: 1675: 1669: 1663: 1643: 1636: 1632: 1631: 1625: 1608: 1602: 1582: 1562: 1555: 1533: 1530: 1527: 1515: 1489: 1486: 1483: 1471: 1468: 1462: 1456: 1436: 1429: 1413: 1393: 1385: 1366: 1363: 1360: 1334: 1326: 1310: 1307: 1304: 1296: 1280: 1266: 1252: 1245:has at least 1232: 1229: 1206: 1203: 1200: 1160: 1140: 1137: 1134: 1094: 1071: 1059: 1039: 1019: 1016: 993: 990: 987: 947: 907: 884: 881: 878: 866: 817: 808: 787: 762: 755:. The number 739: 727: 707: 704: 692: 672: 669: 666: 646: 643: 631: 611: 591: 571: 568: 556: 536: 533: 521: 501: 498: 495: 492: 489: 469: 466: 454: 434: 431: 419: 411: 395: 375: 372: 329: 309: 306: 294: 254: 251: 248: 239: 237: 233: 209: 205: 181: 155: 145: 143: 139: 134: 132: 128: 112: 92: 84: 80: 76: 75:HNN extension 72: 68: 55: 34: 27: 23: 19: 6341: 6335: 6327: 6322: 6310: 6304: 6295: 6289: 6277: 6271: 6259: 6253: 6237: 6231: 6223: 6218: 6209: 6203: 6178: 6174: 6168: 6159: 6153: 6126: 6122: 6112: 6087: 6083: 6077: 6041: 6035: 6008: 6004: 5994: 5978: 5976:T. Delzant. 5972: 5960: 5954: 5942: 5936: 5912:(1): 39–46. 5909: 5905: 5895: 5880: 5875: 5863: 5845: 5839: 5830: 5821: 5812: 5804: 5799: 5787: 5781: 5315: 5314:one defines 5009: 4985: 4949:nontrivial. 4875:free product 4793: 4700: 4513: 4334: 4307: 4299: 3852: 3543:Cayley graph 3311:Cayley graph 3232: 3146: 2957: 2929: 2877: 2791: 2790:is called a 2750: 2597: 2593: 2565: 2402:Cayley graph 2335:be a finite 2284: 2196: 1983: 1782:of rank two 1427: 1384:Cayley graph 1323:be a finite 1272: 1173:of edges of 1107:of edges of 1032:has exactly 960:of edges of 920:of edges of 810:Informally, 809: 785: 388:has at most 342:of edges of 240: 208:cell complex 157: 142:torsion-free 135: 48: 21: 18:group theory 15: 6157:H. MĂĽller. 2598:co-boundary 6356:Categories 5631:polycyclic 5010:accessible 4964:free group 4909:with both 4619:where and 4512:The group 4374:The group 3224:in Γ. 2956:is called 2876:is called 2470:denote by 2244:such that 2189:of finite 2165:(that is, 1989:Heinz Hopf 1859:free group 1711:is finite. 1595:, so that 1219:such that 1006:such that 784:is called 685:such that 624:such that 362:the graph 6039:H. Bass. 5958:Z. Sela. 5488:⩽ 5279:⩽ 5122:virtually 4961:virtually 4894:∗ 4841:∞ 4728:we have 4675:subgroups 4607:⟩ 4573:− 4551:⟨ 4494:≠ 4468:≠ 4412:∗ 4215:subgroups 4143:⟩ 4109:− 4087:⟨ 3980:≠ 3954:≠ 3898:∗ 3798:∗ 3741:∗ 3690:∗ 3642:∗ 3514:Γ 3508:Γ 3465:∪ 3309:then the 3250:∗ 3207:∗ 3105:∗ 3055:∗ 2971:∈ 2941:⊆ 2930:A subset 2913:∗ 2878:essential 2859:∗ 2822:δ 2802:Γ 2773:∗ 2734:∗ 2726:δ 2717:δ 2695:∗ 2650:Γ 2607:δ 2577:⊆ 2508:− 2483:∗ 2455:⊆ 2373:Γ 2367:Γ 2320:⊆ 2160:virtually 2062:∞ 2038:∈ 1963:∞ 1919:∞ 1522:Γ 1478:Γ 1355:Γ 1308:⊆ 1230:− 1227:Γ 1204:⊆ 1181:Γ 1138:⩾ 1115:Γ 1075:∞ 1066:Γ 1017:− 1014:Γ 991:⊆ 968:Γ 928:Γ 888:∞ 873:Γ 847:Γ 824:Γ 795:Γ 769:Γ 743:∞ 734:Γ 705:⩽ 699:Γ 670:⩾ 644:⩽ 638:Γ 563:Γ 534:⩽ 528:Γ 493:⩽ 467:⩽ 461:Γ 426:Γ 408:infinite 373:− 370:Γ 350:Γ 307:⩽ 301:Γ 275:Γ 252:⩾ 218:Γ 190:Γ 166:Γ 6242:Archived 6005:Topology 5983:Archived 5741:See also 5652:Dunwoody 5639:Bowditch 5095:Bestvina 5082:Dunwoody 4966:is free. 3677:. Thus 3500:and let 2990:between 2359:and let 2204:A group 2187:subgroup 2103:we have 2080:For any 2018:we have 1995:For any 1931:we have 1811:we have 1778:For the 1739:we have 1714:For the 1656:we have 1347:and let 230:are the 79:subgroup 6195:1025923 6145:0466326 6104:0487104 6027:1838998 5928:0716233 5736:groups. 3541:be the 2596:or the 2400:be the 1382:be the 6193:  6143:  6102:  6025:  5926:  5887:  5733:Gromov 5699:using 4785:action 4534:is an 4437:where 4159:where 4155:is an 3923:where 3585:. Let 3265:where 2592:, the 1889:where 1857:For a 1633:For a 1426:. The 1297:. Let 720:, put 127:action 73:or an 20:, the 5773:Notes 5457:over 5356:) of 4433:as a 4335:Then 4328:be a 4257:is a 4237:then 3995:then 3919:is a 2305:be a 2191:index 1293:be a 1193:with 980:with 859:. If 202:as a 180:graph 5885:ISBN 5731:). 5729:Wall 5529:> 5422:> 5237:has 5125:free 4929:and 4789:tree 4748:> 4483:and 4355:> 4308:Let 4281:> 4261:and 4055:> 4015:and 3969:and 3876:: 3835:> 3428:and 3388:and 3353:> 3285:and 3170:> 3092:and 3010:and 2986:the 2900:and 2285:Let 1916:< 1900:< 1273:Let 885:< 499:< 241:Let 232:ends 158:Let 131:tree 6183:doi 6131:doi 6092:doi 6013:doi 5914:doi 5675:in 5120:is 4677:of 4217:of 4073:If 3880:If 3545:of 3313:of 3233:If 2814:if 2794:in 2792:cut 2622:of 2543:in 2523:of 2404:of 2339:of 2158:is 1575:of 1386:of 1327:of 584:if 447:if 6358:: 6191:MR 6189:. 6179:61 6177:. 6141:MR 6139:. 6127:11 6125:. 6121:. 6100:MR 6098:. 6088:11 6086:. 6065:^ 6050:^ 6023:MR 6021:. 6009:40 6007:. 6003:. 5924:MR 5922:. 5910:30 5908:. 5904:. 5854:^ 5080:. 4646:, 4332:. 4186:, 3850:. 2748:. 2563:. 2309:, 2193:). 1843:1. 1764:2. 807:. 6197:. 6185:: 6147:. 6133:: 6106:. 6094:: 6029:. 6015:: 5930:. 5916:: 5715:4 5683:G 5663:H 5617:H 5597:H 5576:H 5552:G 5532:1 5526:) 5523:H 5520:, 5517:G 5514:( 5511:e 5491:G 5485:H 5465:H 5445:G 5425:1 5419:) 5416:H 5413:, 5410:G 5407:( 5404:e 5384:H 5364:G 5340:) 5337:H 5334:, 5331:G 5328:( 5325:e 5302:G 5282:G 5276:H 5249:G 5225:G 5205:G 5182:G 5162:G 5135:G 5108:G 5068:G 5044:G 5020:G 4996:G 4981:. 4937:B 4917:A 4897:B 4891:A 4888:= 4885:G 4861:G 4838:= 4835:) 4832:G 4829:( 4826:e 4802:G 4771:G 4751:1 4745:) 4742:G 4739:( 4736:e 4716:G 4697:. 4685:H 4659:2 4655:C 4632:1 4628:C 4602:2 4598:C 4594:= 4591:t 4586:1 4582:C 4576:1 4569:t 4564:| 4560:t 4557:, 4554:H 4548:= 4545:G 4521:G 4509:. 4497:K 4491:C 4471:H 4465:C 4445:C 4421:K 4416:C 4408:H 4405:= 4402:G 4382:G 4358:1 4352:) 4349:G 4346:( 4343:e 4316:G 4296:. 4284:1 4278:) 4275:G 4272:( 4269:e 4245:G 4225:H 4199:2 4195:C 4172:1 4168:C 4138:2 4134:C 4130:= 4127:t 4122:1 4118:C 4112:1 4105:t 4100:| 4096:t 4093:, 4090:H 4084:= 4081:G 4070:. 4058:1 4052:) 4049:G 4046:( 4043:e 4023:K 4003:H 3983:K 3977:C 3957:H 3951:C 3931:C 3907:K 3902:C 3894:H 3891:= 3888:G 3864:G 3838:1 3832:) 3829:G 3826:( 3823:e 3803:) 3794:A 3790:, 3787:A 3784:( 3764:K 3744:K 3738:H 3735:= 3732:G 3712:G 3686:A 3665:H 3645:K 3639:H 3636:= 3633:G 3613:G 3593:A 3573:S 3553:G 3529:) 3526:S 3523:, 3520:G 3517:( 3511:= 3488:G 3468:Y 3462:X 3459:= 3456:S 3436:K 3416:H 3396:Y 3376:X 3356:1 3350:) 3347:G 3344:( 3341:e 3321:G 3293:K 3273:H 3253:K 3247:H 3244:= 3241:G 3212:) 3203:A 3199:, 3196:A 3193:( 3173:1 3167:) 3164:G 3161:( 3158:e 3127:A 3101:A 3080:A 3060:) 3051:A 3047:, 3044:A 3041:( 3021:g 3018:A 2998:A 2974:G 2968:g 2944:G 2938:A 2909:A 2888:A 2864:) 2855:A 2851:, 2848:A 2845:( 2825:A 2778:) 2769:A 2765:, 2762:A 2759:( 2730:A 2723:= 2720:A 2691:A 2670:A 2630:A 2610:A 2580:G 2574:A 2551:G 2531:A 2511:A 2505:G 2479:A 2458:G 2452:A 2432:S 2412:G 2388:) 2385:S 2382:, 2379:G 2376:( 2370:= 2347:G 2323:G 2317:S 2293:G 2276:. 2260:W 2256:/ 2252:G 2232:W 2212:G 2173:G 2146:G 2126:2 2123:= 2120:) 2117:G 2114:( 2111:e 2091:G 2077:. 2065:} 2059:, 2056:2 2053:, 2050:1 2047:, 2044:0 2041:{ 2035:) 2032:G 2029:( 2026:e 2006:G 1975:. 1960:= 1957:) 1954:) 1951:X 1948:( 1945:F 1942:( 1939:e 1912:| 1908:X 1904:| 1897:1 1877:) 1874:X 1871:( 1868:F 1840:= 1837:) 1832:2 1827:Z 1822:( 1819:e 1797:2 1792:Z 1761:= 1758:) 1754:Z 1750:( 1747:e 1726:Z 1699:G 1679:0 1676:= 1673:) 1670:G 1667:( 1664:e 1644:G 1612:) 1609:G 1606:( 1603:e 1583:G 1563:S 1540:) 1537:) 1534:S 1531:, 1528:G 1525:( 1519:( 1516:e 1496:) 1493:) 1490:S 1487:, 1484:G 1481:( 1475:( 1472:e 1469:= 1466:) 1463:G 1460:( 1457:e 1437:G 1414:S 1394:G 1370:) 1367:S 1364:, 1361:G 1358:( 1335:G 1311:G 1305:S 1281:G 1253:n 1233:K 1207:K 1201:F 1161:K 1141:0 1135:n 1095:F 1072:= 1069:) 1063:( 1060:e 1040:m 1020:F 994:K 988:F 948:K 908:F 882:m 879:= 876:) 870:( 867:e 827:) 821:( 818:e 772:) 766:( 763:e 740:= 737:) 731:( 728:e 708:n 702:) 696:( 693:e 673:0 667:n 647:n 641:) 635:( 632:e 612:n 592:m 572:m 569:= 566:) 560:( 557:e 537:n 531:) 525:( 522:e 502:m 496:n 490:0 470:m 464:) 458:( 455:e 435:m 432:= 429:) 423:( 420:e 396:n 376:F 330:F 310:n 304:) 298:( 295:e 255:0 249:n 113:G 93:G 56:G 35:G

Index

group theory
finitely generated group
amalgamated free product
HNN extension
subgroup
Bass–Serre theory
action
tree
John R. Stallings
torsion-free
End (graph theory)
graph
topological space
cell complex
ends
ends of a graph
connected components
finitely generated group
generating set
Cayley graph
generating set
finitely generated group
infinite cyclic group
free abelian group
free group
Hans Freudenthal
Heinz Hopf
finitely generated group
finitely generated group
virtually

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