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Exact sequence

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20: 4332: 4115: 1368: 4353: 4321: 4390: 4363: 4343: 1151: 270: 1135: 1363:{\displaystyle {\begin{aligned}0\rightarrow K_{1}\rightarrow {}&A_{1}\rightarrow K_{2}\rightarrow 0,\\0\rightarrow K_{2}\rightarrow {}&A_{2}\rightarrow K_{3}\rightarrow 0,\\&\ \,\vdots \\0\rightarrow K_{n-1}\rightarrow {}&A_{n-1}\rightarrow K_{n}\rightarrow 0,\\\end{aligned}}} 1855: 1577: 1731: 3213: 107: 977: 3861:
If we take a series of short exact sequences linked by chain complexes (that is, a short exact sequence of chain complexes, or from another point of view, a chain complex of short exact sequences), then we can derive from this a
2823: 3302:(This is true for a number of interesting categories, including any abelian category such as the abelian groups; but it is not true for all categories that allow exact sequences, and in particular is not true for the 799: 3377: 3297: 1785: 3085: 2991:
The importance of short exact sequences is underlined by the fact that every exact sequence results from "weaving together" several overlapping short exact sequences. Consider for instance the exact sequence
2731: 864: 661: 1516: 380: 2285: 3689: 1156: 2114: 1425: 2615: 3618: 1679: 2010: 2332: 1667: 955: 3553: 3474: 2467: 1639: 495:. Traditionally, this, along with the single identity element, is denoted 0 (additive notation, usually when the groups are abelian), or denoted 1 (multiplicative notation). 443: 2946:
For non-commutative groups, the splitting lemma does not apply, and one has only the equivalence between the two last conditions, with "the direct sum" replaced with "a
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To understand the definition, it is helpful to consider relatively simple cases where the sequence is of group homomorphisms, is finite, and begins or ends with the
2501: 2398: 2144: 1476: 411: 310: 51: 265:{\displaystyle G_{0}\;{\xrightarrow {\ f_{1}\ }}\;G_{1}\;{\xrightarrow {\ f_{2}\ }}\;G_{2}\;{\xrightarrow {\ f_{3}\ }}\;\cdots \;{\xrightarrow {\ f_{n}\ }}\;G_{n}} 3103: 2557: 3428: 2036: 4393: 1445: 1130:{\displaystyle A_{0}\;\xrightarrow {\ f_{1}\ } \;A_{1}\;\xrightarrow {\ f_{2}\ } \;A_{2}\;\xrightarrow {\ f_{3}\ } \;\cdots \;\xrightarrow {\ f_{n}\ } \;A_{n},} 2751: 3397: 3762: 732: 3329: 1850:{\displaystyle 0\to \mathbf {Z} \mathrel {\overset {2\times }{\longrightarrow }} \mathbf {Z} \longrightarrow \mathbf {Z} /2\mathbf {Z} \to 0} 3225: 2998: 1572:{\displaystyle \mathbf {Z} \mathrel {\overset {2\times }{\,\hookrightarrow }} \mathbf {Z} \twoheadrightarrow \mathbf {Z} /2\mathbf {Z} } 2630: 1744:
and although it looks like an identity function, it is not onto (that is, not an epimorphism) because the odd numbers don't belong to 2
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used in the previous sequence. This latter sequence does differ in the concrete nature of its first object from the previous one as 2
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Suppose in addition that the cokernel of each morphism exists, and is isomorphic to the image of the next morphism in the sequence:
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to be mapped by inclusion (that is, by a monomorphism) as a proper subgroup of itself. Instead the sequence that emerges from the
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Conversely, given any list of overlapping short exact sequences, their middle terms form an exact sequence in the same manner.
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Given any chain complex, its homology can therefore be thought of as a measure of the degree to which it fails to be exact.
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gives conditions under which the middle map in a commutative diagram with exact rows of length 5 is an isomorphism; the
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A long exact sequence is equivalent to a family of short exact sequences in the following sense: Given a long sequence
1378: 1726:{\displaystyle 2\mathbf {Z} \mathrel {\,\hookrightarrow } \mathbf {Z} \twoheadrightarrow \mathbf {Z} /2\mathbf {Z} } 4281: 2570: 19: 3726:
In the theory of abelian categories, short exact sequences are often used as a convenient language to talk about
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of the monomorphism is the kernel of the epimorphism. Essentially "the same" sequence can also be written as
1963: 507:. The image of the leftmost map is 0. Therefore the sequence is exact if and only if the rightmost map (from 4366: 2564:
These homomorphisms are restrictions of similarly defined homomorphisms that form the short exact sequence
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The first sequence may also be written without using special symbols for monomorphism and epimorphism:
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is another example. Long exact sequences induced by short exact sequences are also characteristic of
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is {0}, and the kernel of multiplication by 2 is also {0}, so the sequence is exact at the first
1884: 480: 276: 74: 4306: 3391:).) Then we obtain a commutative diagram in which all the diagonals are short exact sequences: 2508: 2408: 4324: 4190: 4148: 4013: 3992: 3962: 3958: 3875: 3866:(that is, an exact sequence indexed by the natural numbers) on homology by application of the 3734: 3384: 3479: 2343: 1945:
The first and third sequences are somewhat of a special case owing to the infinite nature of
4104: 4050: 3980: 3950: 3396: 3208:{\displaystyle C_{k}\cong \ker(A_{k}\to A_{k+1})\cong \operatorname {im} (A_{k-1}\to A_{k})} 2980: 2157: 586: 90: 82: 2474: 2371: 2122: 1454: 389: 288: 29: 4163: 4158: 3918: 3883: 3851: 3700: 2742: 2621: 711: 3981: 2536: 2018: 1669:
indicates an epimorphism (the map mod 2). This is an exact sequence because the image 2
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The only portion of this diagram that depends on the cokernel condition is the object
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for details on how to re-form the long exact sequence from the short exact sequences.
4408: 4263: 4173: 4153: 3951: 3946: 3889: 3867: 3811: 2039: 900: 534:. Therefore the sequence is exact if and only if the image of the leftmost map (from 492: 54: 4356: 4248: 4168: 4114: 2147: 1950: 1873: 516: 456: 3691:
is ensured. Again taking the example of the category of groups, the fact that im(
4346: 4258: 2961: 2818:{\displaystyle 0\to A\;\xrightarrow {\ f\ } \;B\;\xrightarrow {\ g\ } \;C\to 0,} 574: 547: 4202: 4133: 4092: 3749:?" In the category of groups, this is equivalent to the question, what groups 2976: 2969: 2917: 2403: 908: 570: 460: 445:, i.e., if the image of each homomorphism is equal to the kernel of the next. 4227: 3727: 687: 66: 448:
The sequence of groups and homomorphisms may be either finite or infinite.
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Sequence of homomorphisms such that each kernel equals the preceding image
4212: 4180: 4129: 4036: 794:{\displaystyle C\cong B/\operatorname {im} (f)=B/\operatorname {ker} (g)} 476: 3745:
of a short exact sequence, what possibilities exist for the middle term
3893: 3372:{\displaystyle H/{\left\langle \operatorname {im} f\right\rangle }^{H}} 467:. More generally, the notion of an exact sequence makes sense in any 3761:
as the corresponding factor group? This problem is important in the
3292:{\displaystyle C_{k}\cong \operatorname {coker} (A_{k-2}\to A_{k-1})} 2790: 2769: 1094: 1066: 1031: 996: 840: 827: 638: 625: 231: 201: 164: 127: 3080:{\displaystyle A_{1}\to A_{2}\to A_{3}\to A_{4}\to A_{5}\to A_{6}} 2045:
As a more concrete example of an exact sequence on finite groups:
969:, to distinguish from the special case of a short exact sequence. 18: 2726:{\displaystyle 0\to R/(I\cap J)\to R/I\oplus R/J\to R/(I+J)\to 0} 859:{\displaystyle 0\to A\xrightarrow {f} B\xrightarrow {g} C\to 0\,} 1752:
through this monomorphism is however exactly the same subset of
656:{\displaystyle 0\to A\xrightarrow {f} B\xrightarrow {g} C\to 0.} 4009: 2968:
with two exact rows gives rise to a longer exact sequence. The
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Exact sequences are precisely those chain complexes which are
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is a special case thereof applying to short exact sequences.
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Commutative Algebra: with a View Toward Algebraic Geometry
3703:, which coincides with its conjugate closure; thus coker( 2953:
In both cases, one says that such a short exact sequence
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As established above, for any such short exact sequence,
515:) has kernel {0}; that is, if and only if that map is a 375:{\displaystyle \operatorname {im} (f_{i})=\ker(f_{i+1})} 3436: 3409: 602:
Short exact sequences are exact sequences of the form
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that transform exact sequences into exact sequences.
3626: 3561: 3515: 3482: 3332: 3228: 3106: 3001: 2754: 2633: 2573: 2539: 2511: 2477: 2437: 2411: 2374: 2346: 2302: 2280:{\displaystyle 0\to I\cap J\to I\oplus J\to I+J\to 0} 2231: 2160: 2125: 2054: 2021: 1966: 1788: 1682: 1655: 1627: 1519: 1457: 1433: 1381: 1154: 980: 928: 813: 735: 611: 419: 392: 318: 291: 110: 32: 455:. For example, one could have an exact sequence of 4272: 4236: 4122: 4043: 3846:of this chain complex is trivial. More succinctly: 3684:{\displaystyle 0\to C_{k}\to A_{k}\to C_{k+1}\to 0} 1510:Consider the following sequence of abelian groups: 569:is both a monomorphism and epimorphism (that is, a 3772:Notice that in an exact sequence, the composition 3683: 3612: 3547: 3501: 3468: 3422: 3371: 3291: 3207: 3079: 2817: 2725: 2609: 2551: 2523: 2495: 2461: 2423: 2392: 2358: 2326: 2279: 2176: 2138: 2109:{\displaystyle 1\to C_{n}\to D_{2n}\to C_{2}\to 1} 2108: 2030: 2004: 1849: 1725: 1661: 1633: 1571: 1470: 1439: 1419: 1362: 1129: 949: 858: 793: 655: 437: 405: 374: 304: 264: 45: 3737:is essentially the question "Given the end terms 1420:{\displaystyle K_{i}=\operatorname {im} (f_{i})} 1906:, and the kernel of reducing modulo 2 is also 2 1860:Here 0 denotes the trivial group, the map from 1146:2, we can split it up into the short sequences 965:A general exact sequence is sometimes called a 1776:even though the two are isomorphic as groups. 4021: 2610:{\displaystyle 0\to R\to R\oplus R\to R\to 0} 674:is an epimorphism. Furthermore, the image of 8: 1649:is a monomorphism, and the two-headed arrow 1598:. The second homomorphism maps each element 3613:{\displaystyle A_{k-1}\to A_{k}\to A_{k+1}} 1933:, so the sequence is exact at the position 451:A similar definition can be made for other 101:In the context of group theory, a sequence 4389: 4362: 4028: 4014: 4006: 2802: 2785: 2781: 2764: 1113: 1089: 1085: 1061: 1050: 1026: 1015: 991: 251: 225: 221: 195: 184: 158: 147: 121: 3663: 3650: 3637: 3625: 3598: 3585: 3566: 3560: 3533: 3520: 3514: 3487: 3481: 3454: 3441: 3435: 3414: 3408: 3363: 3342: 3336: 3331: 3274: 3255: 3233: 3227: 3196: 3177: 3146: 3133: 3111: 3105: 3071: 3058: 3045: 3032: 3019: 3006: 3000: 2753: 2745:states that, for a short exact sequence 2697: 2683: 2669: 2643: 2632: 2572: 2538: 2510: 2476: 2436: 2410: 2373: 2345: 2301: 2230: 2165: 2159: 2130: 2124: 2094: 2078: 2065: 2053: 2020: 1988: 1965: 1925:, and the kernel of the zero map is also 1910:, so the sequence is exact at the second 1868:is multiplication by 2, and the map from 1836: 1828: 1823: 1815: 1800: 1795: 1787: 1718: 1710: 1705: 1697: 1692: 1691: 1686: 1681: 1654: 1626: 1582:The first homomorphism maps each element 1564: 1556: 1551: 1543: 1528: 1525: 1520: 1518: 1462: 1456: 1432: 1408: 1386: 1380: 1341: 1322: 1314: 1299: 1281: 1258: 1245: 1237: 1228: 1199: 1186: 1178: 1169: 1155: 1153: 1118: 1102: 1074: 1055: 1039: 1020: 1004: 985: 979: 927: 855: 812: 771: 745: 734: 610: 561:→ 0 is exact if and only if the map from 546:; that is, if and only if that map is an 418: 397: 391: 357: 332: 317: 296: 290: 256: 239: 226: 209: 196: 189: 172: 159: 152: 135: 122: 115: 109: 37: 31: 3695:) is the kernel of some homomorphism on 2825:the following conditions are equivalent. 2296:-modules, where the module homomorphism 1486:is a long exact sequence if and only if 530:→ 0. The kernel of the rightmost map is 3910: 3090:which implies that there exist objects 2038:as these groups are not supposed to be 2005:{\displaystyle 1\to N\to G\to G/N\to 1} 710:as the corresponding factor object (or 1902:the image of multiplication by 2 is 2 1887:2. This is indeed an exact sequence: 81:, and, more generally, objects of an 23:Illustration of an exact sequence of 7: 3987:. Springer-Verlag New York. p.  3919:"exact sequence in nLab, Remark 2.3" 2327:{\displaystyle I\cap J\to I\oplus J} 2015:(here the trivial group is denoted 1736:In this case the monomorphism is 2 1662:{\displaystyle \twoheadrightarrow } 1478:'s (regardless of the exactness of 1917:the image of reducing modulo 2 is 1494: 14: 1447:. By construction, the sequences 950:{\displaystyle B\cong A\oplus C.} 4388: 4361: 4351: 4341: 4330: 4320: 4319: 4113: 3620:is exact, then the exactness of 3548:{\displaystyle A_{k}\to A_{k+1}} 3469:{\textstyle A_{6}\to C_{7}\to 0} 3430:and the final pair of morphisms 3395: 2462:{\displaystyle I\oplus J\to I+J} 2192:, which is a non-abelian group. 1837: 1824: 1816: 1796: 1719: 1706: 1698: 1687: 1634:{\displaystyle \hookrightarrow } 1610:in the quotient group; that is, 1565: 1552: 1544: 1521: 3810:, so every exact sequence is a 3722:Applications of exact sequences 2196:Intersection and sum of modules 1641:indicates that the map 2× from 1490:are all short exact sequences. 899:. It follows that if these are 875:if there exists a homomorphism 3675: 3656: 3643: 3630: 3591: 3578: 3526: 3476:. If there exists any object 3460: 3447: 3286: 3267: 3248: 3202: 3189: 3170: 3158: 3139: 3126: 3064: 3051: 3038: 3025: 3012: 2806: 2758: 2717: 2714: 2702: 2691: 2663: 2660: 2648: 2637: 2624:yields another exact sequence 2601: 2595: 2583: 2577: 2490: 2478: 2447: 2387: 2375: 2312: 2271: 2259: 2247: 2235: 2100: 2087: 2071: 2058: 1996: 1982: 1976: 1970: 1883:is given by reducing integers 1841: 1820: 1802: 1792: 1702: 1693: 1656: 1628: 1548: 1529: 1414: 1401: 1347: 1334: 1311: 1292: 1264: 1251: 1234: 1221: 1205: 1192: 1175: 1162: 849: 817: 788: 782: 762: 756: 647: 615: 369: 350: 338: 325: 69:between objects (for example, 1: 3707:) is isomorphic to the image 3957:. Berlin: Springer. p.  682:. It is helpful to think of 553:Therefore, the sequence 0 → 483:, where it is widely used. 438:{\displaystyle 1\leq i<n} 1949:. It is not possible for a 522:Consider the dual sequence 519:(injective, or one-to-one). 89:of one morphism equals the 4436: 4282:Banach fixed-point theorem 3097:in the category such that 887:such that the composition 678:is equal to the kernel of 499:Consider the sequence 0 → 4315: 4111: 3757:as a normal subgroup and 2524:{\displaystyle I\oplus J} 2424:{\displaystyle I\oplus J} 1955:first isomorphism theorem 1891:the image of the map 0 → 804:The short exact sequence 382:. The sequence is called 3767:Outer automorphism group 3763:classification of groups 3715:) of the next morphism. 2896:There exists a morphism 2863:There exists a morphism 2830:There exists a morphism 2290:is an exact sequence of 726:inducing an isomorphism 479:, and more specially in 3880:Mayer–Vietoris sequence 3823:-images of elements of 3502:{\displaystyle A_{k+1}} 2431:, and the homomorphism 2359:{\displaystyle I\cap J} 1772:is not the same set as 1586:in the set of integers 895:is the identity map on 386:if it is exact at each 4337:Mathematics portal 4237:Metrics and properties 4223:Second-countable space 3685: 3614: 3549: 3503: 3470: 3424: 3373: 3293: 3209: 3081: 2819: 2727: 2611: 2553: 2525: 2497: 2463: 2425: 2394: 2360: 2328: 2281: 2178: 2177:{\displaystyle D_{2n}} 2140: 2110: 2032: 2006: 1851: 1727: 1663: 1635: 1621:. Here the hook arrow 1573: 1472: 1441: 1421: 1364: 1131: 951: 860: 795: 670:is a monomorphism and 657: 585:(this always holds in 550:(surjective, or onto). 439: 407: 376: 306: 266: 58: 47: 3699:implies that it is a 3686: 3615: 3550: 3504: 3471: 3425: 3374: 3294: 3210: 3082: 2820: 2728: 2612: 2554: 2526: 2498: 2496:{\displaystyle (x,y)} 2464: 2426: 2395: 2393:{\displaystyle (x,x)} 2361: 2329: 2282: 2179: 2141: 2139:{\displaystyle C_{n}} 2111: 2033: 2007: 1852: 1728: 1664: 1636: 1574: 1473: 1471:{\displaystyle K_{i}} 1442: 1422: 1365: 1132: 952: 907:is isomorphic to the 861: 796: 658: 573:), and so usually an 440: 408: 406:{\displaystyle G_{i}} 377: 307: 305:{\displaystyle G_{i}} 267: 48: 46:{\displaystyle G_{i}} 22: 4292:Invariance of domain 4244:Euler characteristic 4218:Bundle (mathematics) 3947:Spanier, Edwin Henry 3814:. Furthermore, only 3730:and factor objects. 3624: 3559: 3513: 3480: 3434: 3407: 3330: 3226: 3104: 2999: 2752: 2631: 2571: 2537: 2509: 2475: 2435: 2409: 2372: 2344: 2300: 2229: 2158: 2123: 2052: 2019: 1964: 1786: 1680: 1653: 1625: 1517: 1455: 1431: 1379: 1152: 978: 926: 811: 733: 609: 598:Short exact sequence 465:module homomorphisms 463:, or of modules and 453:algebraic structures 417: 390: 316: 289: 108: 30: 4420:Additive categories 4415:Homological algebra 4302:Tychonoff's theorem 4297:Poincaré conjecture 4051:General (point-set) 3864:long exact sequence 3832:are mapped to 0 by 2972:is a special case. 2966:commutative diagram 2887:is the identity on 2854:is the identity on 2800: 2779: 2552:{\displaystyle x-y} 1506:Integers modulo two 1111: 1083: 1048: 1013: 967:long exact sequence 961:Long exact sequence 844: 831: 642: 629: 277:group homomorphisms 248: 218: 181: 144: 4287:De Rham cohomology 4208:Polyhedral complex 4198:Simplicial complex 3953:Algebraic Topology 3872:algebraic topology 3681: 3610: 3545: 3499: 3466: 3423:{\textstyle C_{7}} 3420: 3379:, the quotient of 3369: 3304:category of groups 3289: 3205: 3077: 2948:semidirect product 2815: 2723: 2607: 2549: 2521: 2493: 2469:maps each element 2459: 2421: 2390: 2356: 2334:maps each element 2324: 2277: 2174: 2136: 2106: 2031:{\displaystyle 1,} 2028: 2002: 1847: 1723: 1659: 1631: 1569: 1468: 1437: 1417: 1360: 1358: 1127: 947: 856: 791: 653: 481:abelian categories 435: 403: 372: 302: 262: 59: 43: 4402: 4401: 4191:fundamental group 3876:relative homology 3870:. It comes up in 3735:extension problem 3385:conjugate closure 3306:, in which coker( 2801: 2799: 2793: 2780: 2778: 2772: 1813: 1541: 1451:are exact at the 1440:{\displaystyle i} 1280: 1112: 1110: 1097: 1084: 1082: 1069: 1049: 1047: 1034: 1014: 1012: 999: 845: 832: 643: 630: 249: 247: 234: 219: 217: 204: 182: 180: 167: 145: 143: 130: 65:is a sequence of 4427: 4392: 4391: 4365: 4364: 4355: 4345: 4335: 4334: 4323: 4322: 4117: 4030: 4023: 4016: 4007: 4002: 3986: 3972: 3956: 3933: 3932: 3930: 3929: 3915: 3884:derived functors 3874:in the study of 3690: 3688: 3687: 3682: 3674: 3673: 3655: 3654: 3642: 3641: 3619: 3617: 3616: 3611: 3609: 3608: 3590: 3589: 3577: 3576: 3554: 3552: 3551: 3546: 3544: 3543: 3525: 3524: 3508: 3506: 3505: 3500: 3498: 3497: 3475: 3473: 3472: 3467: 3459: 3458: 3446: 3445: 3429: 3427: 3426: 3421: 3419: 3418: 3399: 3378: 3376: 3375: 3370: 3368: 3367: 3362: 3361: 3357: 3340: 3298: 3296: 3295: 3290: 3285: 3284: 3266: 3265: 3238: 3237: 3214: 3212: 3211: 3206: 3201: 3200: 3188: 3187: 3157: 3156: 3138: 3137: 3116: 3115: 3086: 3084: 3083: 3078: 3076: 3075: 3063: 3062: 3050: 3049: 3037: 3036: 3024: 3023: 3011: 3010: 2981:short five lemma 2941: 2930: 2915: 2909: 2892: 2886: 2876: 2859: 2853: 2843: 2824: 2822: 2821: 2816: 2797: 2791: 2786: 2776: 2770: 2765: 2732: 2730: 2729: 2724: 2701: 2687: 2673: 2647: 2622:quotient modules 2616: 2614: 2613: 2608: 2560: 2558: 2556: 2555: 2550: 2530: 2528: 2527: 2522: 2504: 2502: 2500: 2499: 2494: 2468: 2466: 2465: 2460: 2430: 2428: 2427: 2422: 2401: 2399: 2397: 2396: 2391: 2365: 2363: 2362: 2357: 2339: 2333: 2331: 2330: 2325: 2295: 2286: 2284: 2283: 2278: 2221: 2211: 2205: 2183: 2181: 2180: 2175: 2173: 2172: 2145: 2143: 2142: 2137: 2135: 2134: 2115: 2113: 2112: 2107: 2099: 2098: 2086: 2085: 2070: 2069: 2037: 2035: 2034: 2029: 2011: 2009: 2008: 2003: 1992: 1856: 1854: 1853: 1848: 1840: 1832: 1827: 1819: 1814: 1812: 1801: 1799: 1756:as the image of 1748:. The image of 2 1732: 1730: 1729: 1724: 1722: 1714: 1709: 1701: 1696: 1690: 1668: 1666: 1665: 1660: 1640: 1638: 1637: 1632: 1620: 1590:to the element 2 1578: 1576: 1575: 1570: 1568: 1560: 1555: 1547: 1542: 1540: 1532: 1526: 1524: 1482:). Furthermore, 1477: 1475: 1474: 1469: 1467: 1466: 1446: 1444: 1443: 1438: 1426: 1424: 1423: 1418: 1413: 1412: 1391: 1390: 1369: 1367: 1366: 1361: 1359: 1346: 1345: 1333: 1332: 1315: 1310: 1309: 1278: 1276: 1263: 1262: 1250: 1249: 1238: 1233: 1232: 1204: 1203: 1191: 1190: 1179: 1174: 1173: 1136: 1134: 1133: 1128: 1123: 1122: 1108: 1107: 1106: 1095: 1090: 1080: 1079: 1078: 1067: 1062: 1060: 1059: 1045: 1044: 1043: 1032: 1027: 1025: 1024: 1010: 1009: 1008: 997: 992: 990: 989: 956: 954: 953: 948: 865: 863: 862: 857: 836: 823: 800: 798: 797: 792: 775: 749: 662: 660: 659: 654: 634: 621: 587:exact categories 444: 442: 441: 436: 412: 410: 409: 404: 402: 401: 381: 379: 378: 373: 368: 367: 337: 336: 311: 309: 308: 303: 301: 300: 271: 269: 268: 263: 261: 260: 250: 245: 244: 243: 232: 227: 220: 215: 214: 213: 202: 197: 194: 193: 183: 178: 177: 176: 165: 160: 157: 156: 146: 141: 140: 139: 128: 123: 120: 119: 85:) such that the 83:abelian category 52: 50: 49: 44: 42: 41: 4435: 4434: 4430: 4429: 4428: 4426: 4425: 4424: 4405: 4404: 4403: 4398: 4329: 4311: 4307:Urysohn's lemma 4268: 4232: 4118: 4109: 4081:low-dimensional 4039: 4034: 3999: 3977:Eisenbud, David 3975: 3969: 3945: 3937: 3936: 3927: 3925: 3917: 3916: 3912: 3902: 3841: 3831: 3822: 3809: 3799: 3790: 3781: 3724: 3701:normal subgroup 3659: 3646: 3633: 3622: 3621: 3594: 3581: 3562: 3557: 3556: 3529: 3516: 3511: 3510: 3483: 3478: 3477: 3450: 3437: 3432: 3431: 3410: 3405: 3404: 3347: 3343: 3341: 3328: 3327: 3270: 3251: 3229: 3224: 3223: 3192: 3173: 3142: 3129: 3107: 3102: 3101: 3095: 3067: 3054: 3041: 3028: 3015: 3002: 2997: 2996: 2989: 2932: 2921: 2911: 2897: 2888: 2878: 2864: 2855: 2845: 2831: 2750: 2749: 2743:splitting lemma 2739: 2629: 2628: 2569: 2568: 2535: 2534: 2532: 2507: 2506: 2473: 2472: 2470: 2433: 2432: 2407: 2406: 2370: 2369: 2367: 2366:to the element 2342: 2341: 2335: 2298: 2297: 2291: 2227: 2226: 2217: 2207: 2201: 2198: 2161: 2156: 2155: 2126: 2121: 2120: 2090: 2074: 2061: 2050: 2049: 2017: 2016: 1962: 1961: 1805: 1784: 1783: 1678: 1677: 1651: 1650: 1623: 1622: 1611: 1533: 1527: 1515: 1514: 1508: 1503: 1458: 1453: 1452: 1429: 1428: 1404: 1382: 1377: 1376: 1357: 1356: 1337: 1318: 1316: 1295: 1286: 1285: 1274: 1273: 1254: 1241: 1239: 1224: 1215: 1214: 1195: 1182: 1180: 1165: 1150: 1149: 1114: 1098: 1070: 1051: 1035: 1016: 1000: 981: 976: 975: 963: 924: 923: 809: 808: 731: 730: 607: 606: 600: 489: 415: 414: 393: 388: 387: 353: 328: 314: 313: 292: 287: 286: 252: 235: 205: 185: 168: 148: 131: 111: 106: 105: 99: 33: 28: 27: 17: 12: 11: 5: 4433: 4431: 4423: 4422: 4417: 4407: 4406: 4400: 4399: 4397: 4396: 4386: 4385: 4384: 4379: 4374: 4359: 4349: 4339: 4327: 4316: 4313: 4312: 4310: 4309: 4304: 4299: 4294: 4289: 4284: 4278: 4276: 4270: 4269: 4267: 4266: 4261: 4256: 4254:Winding number 4251: 4246: 4240: 4238: 4234: 4233: 4231: 4230: 4225: 4220: 4215: 4210: 4205: 4200: 4195: 4194: 4193: 4188: 4186:homotopy group 4178: 4177: 4176: 4171: 4166: 4161: 4156: 4146: 4141: 4136: 4126: 4124: 4120: 4119: 4112: 4110: 4108: 4107: 4102: 4097: 4096: 4095: 4085: 4084: 4083: 4073: 4068: 4063: 4058: 4053: 4047: 4045: 4041: 4040: 4035: 4033: 4032: 4025: 4018: 4010: 4004: 4003: 3997: 3973: 3967: 3942: 3941: 3935: 3934: 3909: 3908: 3907: 3906: 3901: 3898: 3890:Exact functors 3856: 3855: 3836: 3827: 3818: 3804: 3795: 3786: 3776: 3723: 3720: 3680: 3677: 3672: 3669: 3666: 3662: 3658: 3653: 3649: 3645: 3640: 3636: 3632: 3629: 3607: 3604: 3601: 3597: 3593: 3588: 3584: 3580: 3575: 3572: 3569: 3565: 3542: 3539: 3536: 3532: 3528: 3523: 3519: 3496: 3493: 3490: 3486: 3465: 3462: 3457: 3453: 3449: 3444: 3440: 3417: 3413: 3401: 3400: 3366: 3360: 3356: 3353: 3350: 3346: 3339: 3335: 3300: 3299: 3288: 3283: 3280: 3277: 3273: 3269: 3264: 3261: 3258: 3254: 3250: 3247: 3244: 3241: 3236: 3232: 3217: 3216: 3204: 3199: 3195: 3191: 3186: 3183: 3180: 3176: 3172: 3169: 3166: 3163: 3160: 3155: 3152: 3149: 3145: 3141: 3136: 3132: 3128: 3125: 3122: 3119: 3114: 3110: 3093: 3088: 3087: 3074: 3070: 3066: 3061: 3057: 3053: 3048: 3044: 3040: 3035: 3031: 3027: 3022: 3018: 3014: 3009: 3005: 2988: 2985: 2944: 2943: 2894: 2861: 2827: 2826: 2814: 2811: 2808: 2805: 2796: 2789: 2784: 2775: 2768: 2763: 2760: 2757: 2738: 2735: 2734: 2733: 2722: 2719: 2716: 2713: 2710: 2707: 2704: 2700: 2696: 2693: 2690: 2686: 2682: 2679: 2676: 2672: 2668: 2665: 2662: 2659: 2656: 2653: 2650: 2646: 2642: 2639: 2636: 2618: 2617: 2606: 2603: 2600: 2597: 2594: 2591: 2588: 2585: 2582: 2579: 2576: 2548: 2545: 2542: 2520: 2517: 2514: 2492: 2489: 2486: 2483: 2480: 2458: 2455: 2452: 2449: 2446: 2443: 2440: 2420: 2417: 2414: 2389: 2386: 2383: 2380: 2377: 2355: 2352: 2349: 2323: 2320: 2317: 2314: 2311: 2308: 2305: 2288: 2287: 2276: 2273: 2270: 2267: 2264: 2261: 2258: 2255: 2252: 2249: 2246: 2243: 2240: 2237: 2234: 2197: 2194: 2186:dihedral group 2171: 2168: 2164: 2133: 2129: 2117: 2116: 2105: 2102: 2097: 2093: 2089: 2084: 2081: 2077: 2073: 2068: 2064: 2060: 2057: 2027: 2024: 2013: 2012: 2001: 1998: 1995: 1991: 1987: 1984: 1981: 1978: 1975: 1972: 1969: 1943: 1942: 1915: 1900: 1858: 1857: 1846: 1843: 1839: 1835: 1831: 1826: 1822: 1818: 1811: 1808: 1804: 1798: 1794: 1791: 1734: 1733: 1721: 1717: 1713: 1708: 1704: 1700: 1695: 1689: 1685: 1658: 1630: 1606:to an element 1580: 1579: 1567: 1563: 1559: 1554: 1550: 1546: 1539: 1536: 1531: 1523: 1507: 1504: 1502: 1499: 1465: 1461: 1436: 1416: 1411: 1407: 1403: 1400: 1397: 1394: 1389: 1385: 1355: 1352: 1349: 1344: 1340: 1336: 1331: 1328: 1325: 1321: 1317: 1313: 1308: 1305: 1302: 1298: 1294: 1291: 1288: 1287: 1284: 1277: 1275: 1272: 1269: 1266: 1261: 1257: 1253: 1248: 1244: 1240: 1236: 1231: 1227: 1223: 1220: 1217: 1216: 1213: 1210: 1207: 1202: 1198: 1194: 1189: 1185: 1181: 1177: 1172: 1168: 1164: 1161: 1158: 1157: 1126: 1121: 1117: 1105: 1101: 1093: 1088: 1077: 1073: 1065: 1058: 1054: 1042: 1038: 1030: 1023: 1019: 1007: 1003: 995: 988: 984: 962: 959: 958: 957: 946: 943: 940: 937: 934: 931: 901:abelian groups 867: 866: 854: 851: 848: 843: 839: 835: 830: 826: 822: 819: 816: 802: 801: 790: 787: 784: 781: 778: 774: 770: 767: 764: 761: 758: 755: 752: 748: 744: 741: 738: 664: 663: 652: 649: 646: 641: 637: 633: 628: 624: 620: 617: 614: 599: 596: 595: 594: 551: 520: 488: 485: 434: 431: 428: 425: 422: 400: 396: 371: 366: 363: 360: 356: 352: 349: 346: 343: 340: 335: 331: 327: 324: 321: 299: 295: 279:is said to be 275:of groups and 273: 272: 259: 255: 242: 238: 230: 224: 212: 208: 200: 192: 188: 175: 171: 163: 155: 151: 138: 134: 126: 118: 114: 98: 95: 63:exact sequence 55:Euler diagrams 40: 36: 15: 13: 10: 9: 6: 4: 3: 2: 4432: 4421: 4418: 4416: 4413: 4412: 4410: 4395: 4387: 4383: 4380: 4378: 4375: 4373: 4370: 4369: 4368: 4360: 4358: 4354: 4350: 4348: 4344: 4340: 4338: 4333: 4328: 4326: 4318: 4317: 4314: 4308: 4305: 4303: 4300: 4298: 4295: 4293: 4290: 4288: 4285: 4283: 4280: 4279: 4277: 4275: 4271: 4265: 4264:Orientability 4262: 4260: 4257: 4255: 4252: 4250: 4247: 4245: 4242: 4241: 4239: 4235: 4229: 4226: 4224: 4221: 4219: 4216: 4214: 4211: 4209: 4206: 4204: 4201: 4199: 4196: 4192: 4189: 4187: 4184: 4183: 4182: 4179: 4175: 4172: 4170: 4167: 4165: 4162: 4160: 4157: 4155: 4152: 4151: 4150: 4147: 4145: 4142: 4140: 4137: 4135: 4131: 4128: 4127: 4125: 4121: 4116: 4106: 4103: 4101: 4100:Set-theoretic 4098: 4094: 4091: 4090: 4089: 4086: 4082: 4079: 4078: 4077: 4074: 4072: 4069: 4067: 4064: 4062: 4061:Combinatorial 4059: 4057: 4054: 4052: 4049: 4048: 4046: 4042: 4038: 4031: 4026: 4024: 4019: 4017: 4012: 4011: 4008: 4000: 3998:0-387-94269-6 3994: 3990: 3985: 3984: 3978: 3974: 3970: 3968:0-387-94426-5 3964: 3960: 3955: 3954: 3948: 3944: 3943: 3939: 3938: 3924: 3920: 3914: 3911: 3904: 3903: 3899: 3897: 3895: 3891: 3887: 3885: 3881: 3877: 3873: 3869: 3868:zig-zag lemma 3865: 3859: 3853: 3849: 3848: 3847: 3845: 3839: 3835: 3830: 3826: 3821: 3817: 3813: 3812:chain complex 3807: 3803: 3798: 3794: 3789: 3785: 3779: 3775: 3770: 3768: 3764: 3760: 3756: 3752: 3748: 3744: 3740: 3736: 3731: 3729: 3721: 3719: 3716: 3714: 3710: 3706: 3702: 3698: 3694: 3678: 3670: 3667: 3664: 3660: 3651: 3647: 3638: 3634: 3627: 3605: 3602: 3599: 3595: 3586: 3582: 3573: 3570: 3567: 3563: 3540: 3537: 3534: 3530: 3521: 3517: 3509:and morphism 3494: 3491: 3488: 3484: 3463: 3455: 3451: 3442: 3438: 3415: 3411: 3398: 3394: 3393: 3392: 3390: 3386: 3382: 3364: 3358: 3354: 3351: 3348: 3344: 3337: 3333: 3325: 3321: 3317: 3313: 3309: 3305: 3281: 3278: 3275: 3271: 3262: 3259: 3256: 3252: 3245: 3242: 3239: 3234: 3230: 3222: 3221: 3220: 3197: 3193: 3184: 3181: 3178: 3174: 3167: 3164: 3161: 3153: 3150: 3147: 3143: 3134: 3130: 3123: 3120: 3117: 3112: 3108: 3100: 3099: 3098: 3096: 3072: 3068: 3059: 3055: 3046: 3042: 3033: 3029: 3020: 3016: 3007: 3003: 2995: 2994: 2993: 2987:Weaving lemma 2986: 2984: 2982: 2978: 2973: 2971: 2967: 2963: 2958: 2956: 2951: 2949: 2939: 2935: 2928: 2924: 2919: 2914: 2908: 2904: 2900: 2895: 2891: 2885: 2881: 2875: 2871: 2867: 2862: 2858: 2852: 2848: 2842: 2838: 2834: 2829: 2828: 2812: 2809: 2803: 2794: 2787: 2782: 2773: 2766: 2761: 2755: 2748: 2747: 2746: 2744: 2736: 2720: 2711: 2708: 2705: 2698: 2694: 2688: 2684: 2680: 2677: 2674: 2670: 2666: 2657: 2654: 2651: 2644: 2640: 2634: 2627: 2626: 2625: 2623: 2604: 2598: 2592: 2589: 2586: 2580: 2574: 2567: 2566: 2565: 2562: 2546: 2543: 2540: 2518: 2515: 2512: 2487: 2484: 2481: 2456: 2453: 2450: 2444: 2441: 2438: 2418: 2415: 2412: 2405: 2384: 2381: 2378: 2353: 2350: 2347: 2338: 2321: 2318: 2315: 2309: 2306: 2303: 2294: 2274: 2268: 2265: 2262: 2256: 2253: 2250: 2244: 2241: 2238: 2232: 2225: 2224: 2223: 2220: 2215: 2210: 2204: 2195: 2193: 2191: 2187: 2169: 2166: 2162: 2153: 2149: 2131: 2127: 2103: 2095: 2091: 2082: 2079: 2075: 2066: 2062: 2055: 2048: 2047: 2046: 2043: 2041: 2025: 2022: 1999: 1993: 1989: 1985: 1979: 1973: 1967: 1960: 1959: 1958: 1956: 1952: 1948: 1940: 1936: 1932: 1928: 1924: 1920: 1916: 1913: 1909: 1905: 1901: 1898: 1894: 1890: 1889: 1888: 1886: 1882: 1878: 1875: 1871: 1867: 1863: 1844: 1833: 1829: 1809: 1806: 1789: 1782: 1781: 1780: 1777: 1775: 1771: 1767: 1763: 1759: 1755: 1751: 1747: 1743: 1739: 1715: 1711: 1683: 1676: 1675: 1674: 1672: 1648: 1644: 1618: 1614: 1609: 1605: 1601: 1597: 1593: 1589: 1585: 1561: 1557: 1537: 1534: 1513: 1512: 1511: 1505: 1500: 1498: 1496: 1495:weaving lemma 1491: 1489: 1485: 1481: 1463: 1459: 1450: 1434: 1409: 1405: 1398: 1395: 1392: 1387: 1383: 1373: 1372: 1353: 1350: 1342: 1338: 1329: 1326: 1323: 1319: 1306: 1303: 1300: 1296: 1289: 1282: 1270: 1267: 1259: 1255: 1246: 1242: 1229: 1225: 1218: 1211: 1208: 1200: 1196: 1187: 1183: 1170: 1166: 1159: 1147: 1145: 1140: 1139: 1124: 1119: 1115: 1103: 1099: 1091: 1086: 1075: 1071: 1063: 1056: 1052: 1040: 1036: 1028: 1021: 1017: 1005: 1001: 993: 986: 982: 973: 970: 968: 960: 944: 941: 938: 935: 932: 929: 922: 921: 920: 918: 914: 910: 906: 902: 898: 894: 890: 886: 882: 878: 874: 873: 852: 846: 841: 837: 833: 828: 824: 820: 814: 807: 806: 805: 785: 779: 776: 772: 768: 765: 759: 753: 750: 746: 742: 739: 736: 729: 728: 727: 725: 721: 717: 713: 709: 705: 701: 697: 693: 689: 685: 681: 677: 673: 669: 650: 644: 639: 635: 631: 626: 622: 618: 612: 605: 604: 603: 597: 592: 588: 584: 580: 576: 572: 568: 564: 560: 556: 552: 549: 545: 541: 537: 533: 529: 525: 521: 518: 514: 510: 506: 502: 498: 497: 496: 494: 493:trivial group 486: 484: 482: 478: 474: 470: 466: 462: 458: 457:vector spaces 454: 449: 446: 432: 429: 426: 423: 420: 398: 394: 385: 364: 361: 358: 354: 347: 344: 341: 333: 329: 322: 319: 297: 293: 285: 282: 278: 257: 253: 240: 236: 228: 222: 210: 206: 198: 190: 186: 173: 169: 161: 153: 149: 136: 132: 124: 116: 112: 104: 103: 102: 96: 94: 93:of the next. 92: 88: 84: 80: 76: 72: 68: 64: 56: 38: 34: 26: 21: 4394:Publications 4259:Chern number 4249:Betti number 4132: / 4123:Key concepts 4071:Differential 3982: 3952: 3926:. Retrieved 3922: 3913: 3888: 3863: 3860: 3857: 3837: 3833: 3828: 3824: 3819: 3815: 3805: 3801: 3796: 3792: 3787: 3783: 3777: 3773: 3771: 3758: 3754: 3750: 3746: 3742: 3738: 3732: 3725: 3717: 3712: 3708: 3704: 3696: 3692: 3402: 3388: 3380: 3323: 3319: 3315: 3311: 3307: 3301: 3218: 3091: 3089: 2990: 2974: 2964:shows how a 2959: 2954: 2952: 2945: 2937: 2933: 2926: 2922: 2912: 2906: 2902: 2898: 2889: 2883: 2879: 2873: 2869: 2865: 2856: 2850: 2846: 2840: 2836: 2832: 2740: 2619: 2563: 2336: 2292: 2289: 2218: 2208: 2202: 2199: 2189: 2151: 2148:cyclic group 2118: 2044: 2014: 1951:finite group 1946: 1944: 1938: 1934: 1930: 1926: 1922: 1918: 1911: 1907: 1903: 1896: 1892: 1880: 1876: 1874:factor group 1869: 1865: 1861: 1859: 1778: 1773: 1769: 1765: 1761: 1757: 1753: 1749: 1745: 1741: 1737: 1735: 1670: 1646: 1642: 1616: 1612: 1607: 1603: 1599: 1595: 1591: 1587: 1583: 1581: 1509: 1492: 1487: 1483: 1479: 1448: 1374: 1370: 1148: 1143: 1141: 1137: 974: 971: 966: 964: 916: 912: 904: 896: 892: 888: 884: 880: 876: 870: 868: 803: 723: 719: 715: 707: 703: 699: 695: 691: 683: 679: 675: 671: 667: 665: 601: 590: 582: 578: 566: 562: 558: 554: 543: 542:) is all of 539: 535: 531: 527: 523: 517:monomorphism 512: 508: 504: 500: 490: 487:Simple cases 450: 447: 383: 283: 280: 274: 100: 62: 60: 4357:Wikiversity 4274:Key results 3923:ncatlab.org 3765:. See also 2962:snake lemma 2620:Passing to 575:isomorphism 548:epimorphism 461:linear maps 4409:Categories 4203:CW complex 4144:Continuity 4134:Closed set 4093:cohomology 3928:2021-09-05 3900:References 3728:subobjects 3555:such that 2977:five lemma 2970:nine lemma 2918:direct sum 2910:such that 2877:such that 2844:such that 2737:Properties 2404:direct sum 2216:of a ring 2188:of order 2 1427:for every 909:direct sum 869:is called 698:embedding 571:bimorphism 97:Definition 4382:geometric 4377:algebraic 4228:Cobordism 4164:Hausdorff 4159:connected 4076:Geometric 4066:Continuum 4056:Algebraic 3905:Citations 3842:, so the 3676:→ 3657:→ 3644:→ 3631:→ 3592:→ 3579:→ 3571:− 3527:→ 3461:→ 3448:→ 3352:⁡ 3310:) : 3279:− 3268:→ 3260:− 3246:⁡ 3240:≅ 3190:→ 3182:− 3168:⁡ 3162:≅ 3140:→ 3124:⁡ 3118:≅ 3065:→ 3052:→ 3039:→ 3026:→ 3013:→ 2807:→ 2759:→ 2718:→ 2692:→ 2678:⊕ 2664:→ 2655:∩ 2638:→ 2602:→ 2596:→ 2590:⊕ 2584:→ 2578:→ 2544:− 2516:⊕ 2448:→ 2442:⊕ 2416:⊕ 2351:∩ 2319:⊕ 2313:→ 2307:∩ 2272:→ 2260:→ 2254:⊕ 2248:→ 2242:∩ 2236:→ 2150:of order 2101:→ 2088:→ 2072:→ 2059:→ 1997:→ 1983:→ 1977:→ 1971:→ 1842:→ 1821:⟶ 1810:× 1803:⟶ 1793:→ 1703:↠ 1694:↪ 1657:↠ 1629:↪ 1549:↠ 1538:× 1530:↪ 1399:⁡ 1348:→ 1335:→ 1327:− 1312:→ 1304:− 1293:→ 1283:⋮ 1265:→ 1252:→ 1235:→ 1222:→ 1206:→ 1193:→ 1176:→ 1163:→ 1087:⋯ 939:⊕ 933:≅ 850:→ 818:→ 780:⁡ 754:⁡ 740:≅ 706:, and of 688:subobject 648:→ 616:→ 477:cokernels 424:≤ 348:⁡ 323:⁡ 223:⋯ 67:morphisms 4347:Wikibook 4325:Category 4213:Manifold 4181:Homotopy 4139:Interior 4130:Open set 4088:Homology 4037:Topology 3979:(1995). 3949:(1995). 3894:functors 3844:homology 3800:to 0 in 3359:⟩ 3345:⟨ 2835: : 2788:→ 2767:→ 1760:through 1501:Examples 1092:→ 1064:→ 1029:→ 994:→ 879: : 838:→ 825:→ 712:quotient 636:→ 623:→ 469:category 413:for all 229:→ 199:→ 162:→ 125:→ 4372:general 4174:uniform 4154:compact 4105:Digital 3940:Sources 3852:acyclic 3383:by the 3318:is not 2916:is the 2559:⁠ 2533:⁠ 2503:⁠ 2471:⁠ 2402:of the 2400:⁠ 2368:⁠ 2222:. Then 2212:be two 2184:is the 2146:is the 2040:abelian 1872:to the 722:, with 473:kernels 79:modules 4367:Topics 4169:metric 4044:Fields 3995:  3965:  3878:; the 3387:of im( 3326:) but 2955:splits 2798:  2792:  2777:  2771:  2214:ideals 2119:where 1885:modulo 1375:where 1279:  1109:  1096:  1081:  1068:  1046:  1033:  1011:  998:  246:  233:  216:  203:  179:  166:  142:  129:  91:kernel 71:groups 53:using 25:groups 4149:Space 3791:maps 3753:have 3243:coker 1619:mod 2 1142:with 872:split 702:into 694:with 686:as a 589:like 577:from 471:with 384:exact 281:exact 87:image 75:rings 3993:ISBN 3963:ISBN 3892:are 3741:and 3733:The 3711:/im( 3322:/im( 2975:The 2960:The 2931:and 2741:The 2206:and 2200:Let 2154:and 1957:is 1493:See 915:and 475:and 459:and 430:< 3989:785 3959:179 3121:ker 2950:". 2920:of 2531:to 2505:of 2340:of 2042:). 1864:to 1764:↦ 2 1740:↦ 2 1645:to 1602:in 1594:in 1488:(2) 1484:(1) 1480:(1) 1449:(2) 1371:(2) 1144:n ≥ 1138:(1) 911:of 777:ker 714:), 690:of 591:Set 581:to 565:to 538:to 511:to 345:ker 312:if 61:An 4411:: 3991:. 3961:. 3921:. 3886:. 3840:+1 3808:+2 3782:∘ 3780:+1 3769:. 3349:im 3314:→ 3165:im 2957:. 2905:→ 2901:: 2882:∘ 2872:→ 2868:: 2849:∘ 2839:→ 2561:. 1937:/2 1929:/2 1921:/2 1879:/2 1615:= 1396:im 919:: 903:, 891:∘ 883:→ 751:im 651:0. 593:). 557:→ 526:→ 503:→ 320:im 284:at 77:, 73:, 4029:e 4022:t 4015:v 4001:. 3971:. 3931:. 3854:. 3838:i 3834:f 3829:i 3825:A 3820:i 3816:f 3806:i 3802:A 3797:i 3793:A 3788:i 3784:f 3778:i 3774:f 3759:C 3755:A 3751:B 3747:B 3743:C 3739:A 3713:f 3709:H 3705:f 3697:H 3693:f 3679:0 3671:1 3668:+ 3665:k 3661:C 3652:k 3648:A 3639:k 3635:C 3628:0 3606:1 3603:+ 3600:k 3596:A 3587:k 3583:A 3574:1 3568:k 3564:A 3541:1 3538:+ 3535:k 3531:A 3522:k 3518:A 3495:1 3492:+ 3489:k 3485:A 3464:0 3456:7 3452:C 3443:6 3439:A 3416:7 3412:C 3389:f 3381:H 3365:H 3355:f 3338:/ 3334:H 3324:f 3320:H 3316:H 3312:G 3308:f 3287:) 3282:1 3276:k 3272:A 3263:2 3257:k 3253:A 3249:( 3235:k 3231:C 3215:. 3203:) 3198:k 3194:A 3185:1 3179:k 3175:A 3171:( 3159:) 3154:1 3151:+ 3148:k 3144:A 3135:k 3131:A 3127:( 3113:k 3109:C 3094:k 3092:C 3073:6 3069:A 3060:5 3056:A 3047:4 3043:A 3034:3 3030:A 3021:2 3017:A 3008:1 3004:A 2942:. 2940:) 2938:C 2936:( 2934:u 2929:) 2927:A 2925:( 2923:f 2913:B 2907:B 2903:C 2899:u 2893:. 2890:C 2884:u 2880:g 2874:B 2870:C 2866:u 2860:. 2857:A 2851:f 2847:t 2841:A 2837:B 2833:t 2813:, 2810:0 2804:C 2795:g 2783:B 2774:f 2762:A 2756:0 2721:0 2715:) 2712:J 2709:+ 2706:I 2703:( 2699:/ 2695:R 2689:J 2685:/ 2681:R 2675:I 2671:/ 2667:R 2661:) 2658:J 2652:I 2649:( 2645:/ 2641:R 2635:0 2605:0 2599:R 2593:R 2587:R 2581:R 2575:0 2547:y 2541:x 2519:J 2513:I 2491:) 2488:y 2485:, 2482:x 2479:( 2457:J 2454:+ 2451:I 2445:J 2439:I 2419:J 2413:I 2388:) 2385:x 2382:, 2379:x 2376:( 2354:J 2348:I 2337:x 2322:J 2316:I 2310:J 2304:I 2293:R 2275:0 2269:J 2266:+ 2263:I 2257:J 2251:I 2245:J 2239:I 2233:0 2219:R 2209:J 2203:I 2190:n 2170:n 2167:2 2163:D 2152:n 2132:n 2128:C 2104:1 2096:2 2092:C 2083:n 2080:2 2076:D 2067:n 2063:C 2056:1 2026:, 2023:1 2000:1 1994:N 1990:/ 1986:G 1980:G 1974:N 1968:1 1947:Z 1941:. 1939:Z 1935:Z 1931:Z 1927:Z 1923:Z 1919:Z 1914:. 1912:Z 1908:Z 1904:Z 1899:. 1897:Z 1893:Z 1881:Z 1877:Z 1870:Z 1866:Z 1862:Z 1845:0 1838:Z 1834:2 1830:/ 1825:Z 1817:Z 1807:2 1797:Z 1790:0 1774:Z 1770:Z 1766:n 1762:n 1758:Z 1754:Z 1750:Z 1746:Z 1742:n 1738:n 1720:Z 1716:2 1712:/ 1707:Z 1699:Z 1688:Z 1684:2 1671:Z 1647:Z 1643:Z 1617:i 1613:j 1608:j 1604:Z 1600:i 1596:Z 1592:i 1588:Z 1584:i 1566:Z 1562:2 1558:/ 1553:Z 1545:Z 1535:2 1522:Z 1464:i 1460:K 1435:i 1415:) 1410:i 1406:f 1402:( 1393:= 1388:i 1384:K 1354:, 1351:0 1343:n 1339:K 1330:1 1324:n 1320:A 1307:1 1301:n 1297:K 1290:0 1271:, 1268:0 1260:3 1256:K 1247:2 1243:A 1230:2 1226:K 1219:0 1212:, 1209:0 1201:2 1197:K 1188:1 1184:A 1171:1 1167:K 1160:0 1125:, 1120:n 1116:A 1104:n 1100:f 1076:3 1072:f 1057:2 1053:A 1041:2 1037:f 1022:1 1018:A 1006:1 1002:f 987:0 983:A 945:. 942:C 936:A 930:B 917:C 913:A 905:B 897:C 893:h 889:g 885:B 881:C 877:h 853:0 847:C 842:g 834:B 829:f 821:A 815:0 789:) 786:g 783:( 773:/ 769:B 766:= 763:) 760:f 757:( 747:/ 743:B 737:C 724:g 720:A 718:/ 716:B 708:C 704:B 700:A 696:f 692:B 684:A 680:g 676:f 672:g 668:f 645:C 640:g 632:B 627:f 619:A 613:0 583:Y 579:X 567:Y 563:X 559:Y 555:X 544:C 540:C 536:B 532:C 528:C 524:B 513:B 509:A 505:B 501:A 433:n 427:i 421:1 399:i 395:G 370:) 365:1 362:+ 359:i 355:f 351:( 342:= 339:) 334:i 330:f 326:( 298:i 294:G 258:n 254:G 241:n 237:f 211:3 207:f 191:2 187:G 174:2 170:f 154:1 150:G 137:1 133:f 117:0 113:G 57:. 39:i 35:G

Index

Illustration of an exact sequence of groups using Euler diagrams. Each group is represented by a circle, within which there is a subgroup that is simultaneously the range of the previous homomorphism and the kernel of the next one, because of the exact sequence condition.
groups
Euler diagrams
morphisms
groups
rings
modules
abelian category
image
kernel
group homomorphisms
algebraic structures
vector spaces
linear maps
module homomorphisms
category
kernels
cokernels
abelian categories
trivial group
monomorphism
epimorphism
bimorphism
isomorphism
exact categories
subobject
quotient
split
abelian groups
direct sum

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