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Almost complex manifold

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The converse question, whether the almost complex structure implies the existence of a complex structure is much less trivial, and not true in general. On an arbitrary almost complex manifold one can always find coordinates for which the almost complex structure takes the above canonical form at any
2112: 299:. Only when this local tensor can be patched together to be defined globally does the pointwise linear complex structure yield an almost complex structure, which is then uniquely determined. The possibility of this patching, and therefore existence of an almost complex structure on a manifold 1448:
One easily checks that this map defines an almost complex structure. Thus any complex structure on a manifold yields an almost complex structure, which is said to be 'induced' by the complex structure, and the complex structure is said to be 'compatible with' the almost complex structure.
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The existence of an almost complex structure is a topological question and is relatively easy to answer, as discussed above. The existence of an integrable almost complex structure, on the other hand, is a much more difficult analytic question. For example, it is still not known whether
1300: 2146: = 0. The compatible complex structure is unique, as discussed above. Since the existence of an integrable almost complex structure is equivalent to the existence of a complex structure, this is sometimes taken as the definition of a complex structure. 2149:
There are several other criteria which are equivalent to the vanishing of the Nijenhuis tensor, and which therefore furnish methods for checking the integrability of an almost complex structure (and in fact each of these can be found in the literature):
1173: 628:, we can build exterior powers of the complexified cotangent bundle (which is canonically isomorphic to the bundle of dual spaces of the complexified tangent bundle). The almost complex structure induces the decomposition of each space of 1097: 738: 1900: 910: 1438:{\displaystyle J{\frac {\partial }{\partial z^{\mu }}}=i{\frac {\partial }{\partial z^{\mu }}}\qquad J{\frac {\partial }{\partial {\bar {z}}^{\mu }}}=-i{\frac {\partial }{\partial {\bar {z}}^{\mu }}}.} 2195: 851: 1165: 1676: 2238: 2476:
In each of these equations, the two structures on the right hand side are called compatible when the corresponding construction yields a structure of the type specified. For example,
976: 415: 474: 1284:{\displaystyle J{\frac {\partial }{\partial x^{\mu }}}={\frac {\partial }{\partial y^{\mu }}}\qquad J{\frac {\partial }{\partial y^{\mu }}}=-{\frac {\partial }{\partial x^{\mu }}}} 1864: 191: 1722: 933: 147: 995: 3825: 2716: 3016: 54:
is an almost complex manifold, but there are almost complex manifolds that are not complex manifolds. Almost complex structures have important applications in
3820: 2107:{\displaystyle -(N_{A})_{ij}^{k}=A_{i}^{m}\partial _{m}A_{j}^{k}-A_{j}^{m}\partial _{m}A_{i}^{k}-A_{m}^{k}(\partial _{i}A_{j}^{m}-\partial _{j}A_{i}^{m}).} 638: 3107: 3131: 2259: 1497: 3326: 3196: 2926: 2251:
admits an integrable almost complex structure, despite a long history of ultimately unverified claims. Smoothness issues are important. For
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shows that any even dimensional vector space admits a linear complex structure. Therefore, an even dimensional manifold always admits a
2667: 2118: 3759: 2906: 2883: 3524: 857: 304: 3116: 2776: 2774:; Bazzoni, Giovanni; Goertsches, Oliver; Konstantis, Panagiotis; Rollenske, Sönke (2018). "On the history of the Hopf problem". 3507: 2945: 799:). Thus we may use the almost complex structure to refine the action of the exterior derivative to the forms of definite type 96:
which squares to −1) on each tangent space of the manifold, which varies smoothly on the manifold. In other words, we have a
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An almost complex structure integrates to a complex structure if the half-dimensional subspace is closed under the
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admits an almost complex structure, it must be even-dimensional. This can be seen as follows. Suppose
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is a map which increases the antiholomorphic part of the type by one. These operators are called the
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on the (1, 0)-vector fields of the complexified tangent bundle, and multiplication by −
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admits an almost complex structure. An example for such an almost complex structure is (1 ≤
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The individual expressions on the right depend on the choice of the smooth vector fields
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Any of these conditions implies the existence of a unique compatible complex structure.
1469:. Such coordinates, if they exist, are called 'local holomorphic coordinates for J'. If 17: 3656: 3581: 3551: 3449: 3442: 3382: 3353: 3223: 3218: 3179: 2684: 2631:. If furthermore this half-dimensional space is the annihilator of a nowhere vanishing 2620: 2590: 935:
is a map which increases the holomorphic part of the type by one (takes forms of type (
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is induced by a complex structure, then it is induced by a unique complex structure.
733:{\displaystyle \Omega ^{r}(M)^{\mathbf {C} }=\bigoplus _{p+q=r}\Omega ^{(p,q)}(M).\,} 150: 47: 3769: 3764: 3606: 3573: 3546: 3454: 3095: 2936: 592: 100: 503:
cannot be given an almost complex structure (Ehresmann and Hopf). In the case of
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The Lie bracket of any two (1, 0)-vector fields is again of type (1, 0)
3612: 3601: 3558: 3459: 3060: 2661: 2632: 153: 31: 579:(which is the vector bundle of complexified tangent spaces at each point) into 3837: 3795: 3621: 3534: 3166: 3070: 556: 528: 93: 66: 2847: 507:, the almost complex structure comes from an honest complex structure on the 3651: 3616: 3321: 3208: 2609: 2757: 2738: 2596:. A generalized almost complex structure is a choice of a half-dimensional 2121:, which generalizes the Lie bracket of vector fields, the Nijenhuis tensor 3815: 3810: 3800: 3191: 3012: 2585:. An ordinary almost complex structure is a choice of a half-dimensional 516: 283:(which is just a linear transformation on each tangent space) such that 2981: 2966: 2890:
Information on compatible triples, Kähler and Hermitian manifolds, etc.
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is itself an almost complex manifold. In local holomorphic coordinates
2712:"On the Chern numbers of certain complex and almost complex manifolds" 1457:. In general, however, it is not possible to find coordinates so that 3407: 2577:, which was elaborated in the doctoral dissertations of his students 1877:, but the left side actually depends only on the pointwise values of 484: 107: 2958: 2839: 2824:(1957). "Complex analytic coordinates in almost complex manifolds". 197:. A manifold equipped with an almost complex structure is called an 2790: 2390:
when each structure can be specified by the two others as follows:
2675: – Manifold with Riemannian, complex and symplectic structure 2985: 2496:
whose sections are the almost complex structures compatible to
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has an almost complex structure. One can show that it must be
2943:(1953). "Groupes de Lie et puissances réduites de Steenrod". 1894:
is a tensor. This is also clear from the component formula
905:{\displaystyle {\overline {\partial }}=\pi _{p,q+1}\circ d} 2511:, one can show that a compatible almost complex structure 575:
allows a decomposition of the complexified tangent bundle
2623:. A generalized almost complex structure integrates to a 520: 2913:
Short section which introduces standard basic material.
2681: – Mathematical structure in differential geometry 2657:
Pages displaying short descriptions of redirect targets
2608:. In both cases one demands that the direct sum of the 1477:
around every point then these patch together to form a
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or, for the usual case of an almost complex structure
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giving it a complex structure, which moreover induces
989:, we note that the exterior derivative can be written 2204: 2162: 1903: 1733: 1691: 1532: 1303: 1176: 1117: 998: 957: 921: 860: 808: 641: 427: 365: 161: 119: 515:, when considered as the set of unit norm imaginary 3783: 3742: 3675: 3572: 3468: 3415: 3406: 3242: 3165: 3104: 3024: 2507:Using elementary properties of the symplectic form 2258:, the Newlander–Nirenberg theorem follows from the 571:, respectively), so an almost complex structure on 2232: 2189: 2106: 1858: 1716: 1670: 1437: 1294:(just like a counterclockwise rotation of π/2) or 1283: 1159: 1091: 970: 927: 904: 845: 732: 468: 409: 185: 141: 2692: – Type of manifold in differential geometry 985:Since the sum of all the projections must be the 535:Differential topology of almost complex manifolds 2664: – Characteristic classes of vector bundles 1519:is a tensor field of rank (1, 1), then the 2717:Proceedings of the National Academy of Sciences 2374:. With this understood, the three structures ( 2190:{\displaystyle d=\partial +{\bar {\partial }}} 539:Just as a complex structure on a vector space 2997: 846:{\displaystyle \partial =\pi _{p+1,q}\circ d} 8: 1160:{\displaystyle z^{\mu }=x^{\mu }+iy^{\mu }} 3412: 3004: 2990: 2982: 2899:Differential Analysis on Complex Manifolds 2777:Differential Geometry and Its Applications 2370:, is given by the analogous operation for 1671:{\displaystyle N_{A}(X,Y)=-A^{2}+A(+)-.\,} 496: 487:which admit almost complex structures are 331:. The existence question is then a purely 92:is a linear complex structure (that is, a 2789: 2747: 2737: 2492:•) is a Riemannian metric. The bundle on 2233:{\displaystyle {\bar {\partial }}^{2}=0.} 2218: 2207: 2206: 2203: 2176: 2175: 2161: 2092: 2087: 2077: 2064: 2059: 2049: 2036: 2031: 2018: 2013: 2003: 1993: 1988: 1975: 1970: 1960: 1950: 1945: 1932: 1924: 1914: 1902: 1855: 1738: 1732: 1696: 1690: 1667: 1568: 1537: 1531: 1523:is a tensor field of rank (1,2) given by 1473:admits local holomorphic coordinates for 1423: 1412: 1411: 1401: 1383: 1372: 1371: 1361: 1348: 1335: 1320: 1307: 1302: 1272: 1259: 1244: 1231: 1218: 1205: 1193: 1180: 1175: 1151: 1135: 1122: 1116: 1070: 1043: 1009: 997: 958: 956: 920: 878: 861: 859: 819: 807: 747:) admits a decomposition into a sum of Ω( 729: 699: 677: 663: 662: 646: 640: 448: 432: 426: 389: 370: 364: 160: 124: 118: 2919:Algebraic Geometry, a concise dictionary 2556:2 out of 3 property of the unitary group 2135:states that an almost complex structure 2702: 971:{\displaystyle {\overline {\partial }}} 599:is a vector field of type (0, 1). Thus 410:{\displaystyle J_{ij}=-\delta _{i,j-1}} 1461:takes the canonical form on an entire 469:{\displaystyle J_{ij}=\delta _{i,j+1}} 7: 2921:. Berlin/Boston: Walter De Gruyter. 2627:if the subspace is closed under the 2571:generalized almost complex structure 2562:Generalized almost complex structure 2312:, each induces a bundle isomorphism 1859:{\displaystyle N_{J}(X,Y)=+J(+)-.\,} 1103:Integrable almost complex structures 343:For every integer n, the flat space 770:, there is a canonical projection π 595:of type (1, 0), while a section of 335:one and is fairly well understood. 230:be an almost complex structure. If 2589:of each fiber of the complexified 2296:, and an almost complex structure 2209: 2178: 2169: 2074: 2046: 2000: 1957: 1407: 1403: 1367: 1363: 1341: 1337: 1313: 1309: 1265: 1261: 1237: 1233: 1211: 1207: 1186: 1182: 1072: 1064: 960: 922: 863: 809: 696: 643: 613:on the (0, 1)-vector fields. 25: 2554:These triples are related to the 2361:, •) and the other, denoted 603:corresponds to multiplication by 2604:of the complexified tangent and 664: 305:reduction of the structure group 186:{\displaystyle J\colon TM\to TM} 2946:American Journal of Mathematics 2876:Lectures on Symplectic Geometry 2641:generalized Calabi–Yau manifold 2316:, where the first map, denoted 1357: 1227: 3044:Differentiable/Smooth manifold 2600:subspace of each fiber of the 2484:are compatible if and only if 2212: 2181: 2098: 2042: 1921: 1907: 1849: 1831: 1825: 1822: 1807: 1801: 1786: 1783: 1774: 1762: 1756: 1744: 1661: 1643: 1637: 1634: 1619: 1613: 1598: 1595: 1586: 1574: 1555: 1543: 1417: 1377: 723: 717: 712: 700: 659: 652: 174: 1: 2901:. New York: Springer-Verlag. 2625:generalized complex structure 2139:is integrable if and only if 2800:10.1016/j.difgeo.2017.10.014 2710:Van de Ven, A. (June 1966). 2653:Almost quaternionic manifold 1075: 963: 866: 3750:Classification of manifolds 2668:Frölicher–Nijenhuis bracket 2655: – Concept in geometry 2616:yield the original bundle. 2569:introduced the notion of a 2133:Newlander–Nirenberg theorem 2119:Frölicher–Nijenhuis bracket 307:of the tangent bundle from 3885: 2519:for the Riemannian metric 543:allows a decomposition of 3826:over commutative algebras 1717:{\displaystyle J^{2}=-Id} 1511:on each tangent space of 928:{\displaystyle \partial } 784:) to Ω. We also have the 249:is a real manifold, then 81:be a smooth manifold. An 3542:Riemann curvature tensor 1167:one can define the maps 497:Borel & Serre (1953) 256:is a real number – thus 142:{\displaystyle J^{2}=-1} 83:almost complex structure 44:linear complex structure 18:Almost-complex structure 2517:almost Kähler structure 743:In other words, each Ω( 199:almost complex manifold 42:equipped with a smooth 36:almost complex manifold 3334:Manifold with boundary 3049:Differential structure 2739:10.1073/pnas.55.6.1624 2234: 2191: 2128:is just one-half of . 2108: 1860: 1718: 1672: 1439: 1285: 1161: 1093: 972: 929: 906: 847: 734: 470: 411: 216:-dimensional, and let 187: 143: 61:The concept is due to 2917:Rubei, Elena (2014). 2827:Annals of Mathematics 2535:is integrable, then ( 2235: 2192: 2109: 1861: 1719: 1673: 1507:Given any linear map 1440: 1286: 1162: 1094: 973: 930: 907: 848: 735: 471: 412: 333:algebraic topological 188: 144: 3481:Covariant derivative 3032:Topological manifold 2872:Cannas da Silva, Ana 2202: 2160: 1901: 1731: 1689: 1530: 1496:is then said to be ' 1301: 1174: 1115: 996: 955: 943:) to forms of type ( 919: 858: 806: 639: 425: 363: 271:An easy exercise in 159: 117: 3515:Exterior derivative 3117:Atiyah–Singer index 3066:Riemannian manifold 2820:Newlander, August; 2730:1966PNAS...55.1624V 2690:Symplectic manifold 2502:contractible fibres 2282:is equipped with a 2097: 2069: 2041: 2023: 1998: 1980: 1955: 1937: 980:Dolbeault operators 786:exterior derivative 303:is equivalent to a 149:when regarded as a 56:symplectic geometry 3821:Secondary calculus 3775:Singularity theory 3730:Parallel transport 3498:De Rham cohomology 3137:Generalized Stokes 2941:Serre, Jean-Pierre 2325:, is given by the 2274:Compatible triples 2266:(and less smooth) 2230: 2187: 2104: 2083: 2055: 2027: 2009: 1984: 1966: 1941: 1920: 1856: 1714: 1668: 1435: 1281: 1157: 1089: 1038: 968: 925: 902: 843: 730: 694: 618:differential forms 563:corresponding to + 499:). In particular, 466: 407: 183: 139: 3856: 3855: 3738: 3737: 3503:Differential form 3157:Whitney embedding 3091:Differential form 2928:978-3-11-031622-3 2895:Wells, Raymond O. 2830:. Second Series. 2614:complex conjugate 2606:cotangent bundles 2388:compatible triple 2291:Riemannian metric 2260:Frobenius theorem 2215: 2184: 1430: 1420: 1390: 1380: 1355: 1327: 1279: 1251: 1225: 1200: 1078: 1005: 966: 869: 673: 616:Just as we build 521:complex structure 73:Formal definition 63:Charles Ehresmann 16:(Redirected from 3876: 3869:Smooth manifolds 3848:Stratified space 3806:Fréchet manifold 3520:Interior product 3413: 3110: 3006: 2999: 2992: 2983: 2978: 2932: 2912: 2889: 2867: 2822:Nirenberg, Louis 2812: 2811: 2793: 2768: 2762: 2761: 2751: 2741: 2724:(6): 1624–1627. 2707: 2679:Poisson manifold 2658: 2573:on the manifold 2327:interior product 2239: 2237: 2236: 2231: 2223: 2222: 2217: 2216: 2208: 2196: 2194: 2193: 2188: 2186: 2185: 2177: 2117:In terms of the 2113: 2111: 2110: 2105: 2096: 2091: 2082: 2081: 2068: 2063: 2054: 2053: 2040: 2035: 2022: 2017: 2008: 2007: 1997: 1992: 1979: 1974: 1965: 1964: 1954: 1949: 1936: 1931: 1919: 1918: 1865: 1863: 1862: 1857: 1743: 1742: 1723: 1721: 1720: 1715: 1701: 1700: 1677: 1675: 1674: 1669: 1573: 1572: 1542: 1541: 1521:Nijenhuis tensor 1444: 1442: 1441: 1436: 1431: 1429: 1428: 1427: 1422: 1421: 1413: 1402: 1391: 1389: 1388: 1387: 1382: 1381: 1373: 1362: 1356: 1354: 1353: 1352: 1336: 1328: 1326: 1325: 1324: 1308: 1290: 1288: 1287: 1282: 1280: 1278: 1277: 1276: 1260: 1252: 1250: 1249: 1248: 1232: 1226: 1224: 1223: 1222: 1206: 1201: 1199: 1198: 1197: 1181: 1166: 1164: 1163: 1158: 1156: 1155: 1140: 1139: 1127: 1126: 1109:complex manifold 1098: 1096: 1095: 1090: 1079: 1071: 1054: 1053: 1037: 977: 975: 974: 969: 967: 959: 934: 932: 931: 926: 911: 909: 908: 903: 895: 894: 870: 862: 852: 850: 849: 844: 836: 835: 739: 737: 736: 731: 716: 715: 693: 669: 668: 667: 651: 650: 626:cotangent bundle 523:is known as the 511:. The 6-sphere, 475: 473: 472: 467: 465: 464: 440: 439: 416: 414: 413: 408: 406: 405: 378: 377: 330: 318: 294: 278: 260:must be even if 255: 244: 236: 229: 192: 190: 189: 184: 148: 146: 145: 140: 129: 128: 112: 52:complex manifold 21: 3884: 3883: 3879: 3878: 3877: 3875: 3874: 3873: 3859: 3858: 3857: 3852: 3791:Banach manifold 3784:Generalizations 3779: 3734: 3671: 3568: 3530:Ricci curvature 3486:Cotangent space 3464: 3402: 3244: 3238: 3197:Exponential map 3161: 3106: 3100: 3020: 3010: 2959:10.2307/2372495 2935: 2929: 2916: 2909: 2893: 2886: 2870: 2840:10.2307/1970051 2819: 2816: 2815: 2770: 2769: 2765: 2709: 2708: 2704: 2699: 2673:Kähler manifold 2656: 2649: 2629:Courant bracket 2579:Marco Gualtieri 2564: 2549:Kähler manifold 2467: 2458: 2369: 2349: 2336: 2324: 2284:symplectic form 2276: 2205: 2200: 2199: 2158: 2157: 2144: 2126: 2073: 2045: 1999: 1956: 1910: 1899: 1898: 1893: 1885:, which is why 1734: 1729: 1728: 1692: 1687: 1686: 1564: 1533: 1528: 1527: 1410: 1406: 1370: 1366: 1344: 1340: 1316: 1312: 1299: 1298: 1268: 1264: 1240: 1236: 1214: 1210: 1189: 1185: 1172: 1171: 1147: 1131: 1118: 1113: 1112: 1105: 1039: 994: 993: 953: 952: 917: 916: 874: 856: 855: 815: 804: 803: 779: 695: 658: 642: 637: 636: 622:exterior powers 587:. A section of 537: 444: 428: 423: 422: 385: 366: 361: 360: 341: 320: 308: 292: 284: 276: 250: 238: 231: 217: 157: 156: 120: 115: 114: 110: 75: 40:smooth manifold 28: 27:Smooth manifold 23: 22: 15: 12: 11: 5: 3882: 3880: 3872: 3871: 3861: 3860: 3854: 3853: 3851: 3850: 3845: 3840: 3835: 3830: 3829: 3828: 3818: 3813: 3808: 3803: 3798: 3793: 3787: 3785: 3781: 3780: 3778: 3777: 3772: 3767: 3762: 3757: 3752: 3746: 3744: 3740: 3739: 3736: 3735: 3733: 3732: 3727: 3722: 3717: 3712: 3707: 3702: 3697: 3692: 3687: 3681: 3679: 3673: 3672: 3670: 3669: 3664: 3659: 3654: 3649: 3644: 3639: 3629: 3624: 3619: 3609: 3604: 3599: 3594: 3589: 3584: 3578: 3576: 3570: 3569: 3567: 3566: 3561: 3556: 3555: 3554: 3544: 3539: 3538: 3537: 3527: 3522: 3517: 3512: 3511: 3510: 3500: 3495: 3494: 3493: 3483: 3478: 3472: 3470: 3466: 3465: 3463: 3462: 3457: 3452: 3447: 3446: 3445: 3435: 3430: 3425: 3419: 3417: 3410: 3404: 3403: 3401: 3400: 3395: 3385: 3380: 3366: 3361: 3356: 3351: 3346: 3344:Parallelizable 3341: 3336: 3331: 3330: 3329: 3319: 3314: 3309: 3304: 3299: 3294: 3289: 3284: 3279: 3274: 3264: 3254: 3248: 3246: 3240: 3239: 3237: 3236: 3231: 3226: 3224:Lie derivative 3221: 3219:Integral curve 3216: 3211: 3206: 3205: 3204: 3194: 3189: 3188: 3187: 3180:Diffeomorphism 3177: 3171: 3169: 3163: 3162: 3160: 3159: 3154: 3149: 3144: 3139: 3134: 3129: 3124: 3119: 3113: 3111: 3102: 3101: 3099: 3098: 3093: 3088: 3083: 3078: 3073: 3068: 3063: 3058: 3057: 3056: 3051: 3041: 3040: 3039: 3028: 3026: 3025:Basic concepts 3022: 3021: 3011: 3009: 3008: 3001: 2994: 2986: 2980: 2979: 2953:(3): 409–448. 2933: 2927: 2914: 2907: 2891: 2884: 2868: 2834:(3): 391–404. 2814: 2813: 2772:Agricola, Ilka 2763: 2701: 2700: 2698: 2695: 2694: 2693: 2687: 2685:Rizza manifold 2682: 2676: 2670: 2665: 2659: 2648: 2645: 2591:tangent bundle 2583:Gil Cavalcanti 2563: 2560: 2474: 2473: 2463: 2454: 2441: 2418: 2365: 2345: 2341:) =  2332: 2320: 2275: 2272: 2241: 2240: 2229: 2226: 2221: 2214: 2211: 2197: 2183: 2180: 2174: 2171: 2168: 2165: 2155: 2142: 2124: 2115: 2114: 2103: 2100: 2095: 2090: 2086: 2080: 2076: 2072: 2067: 2062: 2058: 2052: 2048: 2044: 2039: 2034: 2030: 2026: 2021: 2016: 2012: 2006: 2002: 1996: 1991: 1987: 1983: 1978: 1973: 1969: 1963: 1959: 1953: 1948: 1944: 1940: 1935: 1930: 1927: 1923: 1917: 1913: 1909: 1906: 1889: 1867: 1866: 1854: 1851: 1848: 1845: 1842: 1839: 1836: 1833: 1830: 1827: 1824: 1821: 1818: 1815: 1812: 1809: 1806: 1803: 1800: 1797: 1794: 1791: 1788: 1785: 1782: 1779: 1776: 1773: 1770: 1767: 1764: 1761: 1758: 1755: 1752: 1749: 1746: 1741: 1737: 1713: 1710: 1707: 1704: 1699: 1695: 1679: 1678: 1666: 1663: 1660: 1657: 1654: 1651: 1648: 1645: 1642: 1639: 1636: 1633: 1630: 1627: 1624: 1621: 1618: 1615: 1612: 1609: 1606: 1603: 1600: 1597: 1594: 1591: 1588: 1585: 1582: 1579: 1576: 1571: 1567: 1563: 1560: 1557: 1554: 1551: 1548: 1545: 1540: 1536: 1446: 1445: 1434: 1426: 1419: 1416: 1409: 1405: 1400: 1397: 1394: 1386: 1379: 1376: 1369: 1365: 1360: 1351: 1347: 1343: 1339: 1334: 1331: 1323: 1319: 1315: 1311: 1306: 1292: 1291: 1275: 1271: 1267: 1263: 1258: 1255: 1247: 1243: 1239: 1235: 1230: 1221: 1217: 1213: 1209: 1204: 1196: 1192: 1188: 1184: 1179: 1154: 1150: 1146: 1143: 1138: 1134: 1130: 1125: 1121: 1104: 1101: 1100: 1099: 1088: 1085: 1082: 1077: 1074: 1069: 1066: 1063: 1060: 1057: 1052: 1049: 1046: 1042: 1036: 1033: 1030: 1027: 1024: 1021: 1018: 1015: 1012: 1008: 1004: 1001: 965: 962: 924: 913: 912: 901: 898: 893: 890: 887: 884: 881: 877: 873: 868: 865: 853: 842: 839: 834: 831: 828: 825: 822: 818: 814: 811: 771: 741: 740: 728: 725: 722: 719: 714: 711: 708: 705: 702: 698: 692: 689: 686: 683: 680: 676: 672: 666: 661: 657: 654: 649: 645: 536: 533: 509:Riemann sphere 463: 460: 457: 454: 451: 447: 443: 438: 435: 431: 404: 401: 398: 395: 392: 388: 384: 381: 376: 373: 369: 340: 337: 295:at each point 288: 273:linear algebra 195:tangent bundle 182: 179: 176: 173: 170: 167: 164: 138: 135: 132: 127: 123: 74: 71: 69:in the 1940s. 26: 24: 14: 13: 10: 9: 6: 4: 3: 2: 3881: 3870: 3867: 3866: 3864: 3849: 3846: 3844: 3843:Supermanifold 3841: 3839: 3836: 3834: 3831: 3827: 3824: 3823: 3822: 3819: 3817: 3814: 3812: 3809: 3807: 3804: 3802: 3799: 3797: 3794: 3792: 3789: 3788: 3786: 3782: 3776: 3773: 3771: 3768: 3766: 3763: 3761: 3758: 3756: 3753: 3751: 3748: 3747: 3745: 3741: 3731: 3728: 3726: 3723: 3721: 3718: 3716: 3713: 3711: 3708: 3706: 3703: 3701: 3698: 3696: 3693: 3691: 3688: 3686: 3683: 3682: 3680: 3678: 3674: 3668: 3665: 3663: 3660: 3658: 3655: 3653: 3650: 3648: 3645: 3643: 3640: 3638: 3634: 3630: 3628: 3625: 3623: 3620: 3618: 3614: 3610: 3608: 3605: 3603: 3600: 3598: 3595: 3593: 3590: 3588: 3585: 3583: 3580: 3579: 3577: 3575: 3571: 3565: 3564:Wedge product 3562: 3560: 3557: 3553: 3550: 3549: 3548: 3545: 3543: 3540: 3536: 3533: 3532: 3531: 3528: 3526: 3523: 3521: 3518: 3516: 3513: 3509: 3508:Vector-valued 3506: 3505: 3504: 3501: 3499: 3496: 3492: 3489: 3488: 3487: 3484: 3482: 3479: 3477: 3474: 3473: 3471: 3467: 3461: 3458: 3456: 3453: 3451: 3448: 3444: 3441: 3440: 3439: 3438:Tangent space 3436: 3434: 3431: 3429: 3426: 3424: 3421: 3420: 3418: 3414: 3411: 3409: 3405: 3399: 3396: 3394: 3390: 3386: 3384: 3381: 3379: 3375: 3371: 3367: 3365: 3362: 3360: 3357: 3355: 3352: 3350: 3347: 3345: 3342: 3340: 3337: 3335: 3332: 3328: 3325: 3324: 3323: 3320: 3318: 3315: 3313: 3310: 3308: 3305: 3303: 3300: 3298: 3295: 3293: 3290: 3288: 3285: 3283: 3280: 3278: 3275: 3273: 3269: 3265: 3263: 3259: 3255: 3253: 3250: 3249: 3247: 3241: 3235: 3232: 3230: 3227: 3225: 3222: 3220: 3217: 3215: 3212: 3210: 3207: 3203: 3202:in Lie theory 3200: 3199: 3198: 3195: 3193: 3190: 3186: 3183: 3182: 3181: 3178: 3176: 3173: 3172: 3170: 3168: 3164: 3158: 3155: 3153: 3150: 3148: 3145: 3143: 3140: 3138: 3135: 3133: 3130: 3128: 3125: 3123: 3120: 3118: 3115: 3114: 3112: 3109: 3105:Main results 3103: 3097: 3094: 3092: 3089: 3087: 3086:Tangent space 3084: 3082: 3079: 3077: 3074: 3072: 3069: 3067: 3064: 3062: 3059: 3055: 3052: 3050: 3047: 3046: 3045: 3042: 3038: 3035: 3034: 3033: 3030: 3029: 3027: 3023: 3018: 3014: 3007: 3002: 3000: 2995: 2993: 2988: 2987: 2984: 2976: 2972: 2968: 2964: 2960: 2956: 2952: 2948: 2947: 2942: 2938: 2937:Borel, Armand 2934: 2930: 2924: 2920: 2915: 2910: 2908:0-387-90419-0 2904: 2900: 2896: 2892: 2887: 2885:3-540-42195-5 2881: 2877: 2873: 2869: 2865: 2861: 2857: 2853: 2849: 2845: 2841: 2837: 2833: 2829: 2828: 2823: 2818: 2817: 2809: 2805: 2801: 2797: 2792: 2787: 2783: 2779: 2778: 2773: 2767: 2764: 2759: 2755: 2750: 2745: 2740: 2735: 2731: 2727: 2723: 2719: 2718: 2713: 2706: 2703: 2696: 2691: 2688: 2686: 2683: 2680: 2677: 2674: 2671: 2669: 2666: 2663: 2660: 2654: 2651: 2650: 2646: 2644: 2642: 2638: 2634: 2630: 2626: 2622: 2617: 2615: 2611: 2607: 2603: 2599: 2595: 2592: 2588: 2584: 2580: 2576: 2572: 2568: 2567:Nigel Hitchin 2561: 2559: 2557: 2552: 2550: 2546: 2542: 2538: 2534: 2530: 2526: 2522: 2518: 2514: 2510: 2505: 2503: 2499: 2495: 2491: 2487: 2483: 2479: 2471: 2466: 2462: 2457: 2453: 2449: 2445: 2442: 2439: 2435: 2431: 2427: 2423: 2419: 2416: 2412: 2408: 2404: 2400: 2396: 2393: 2392: 2391: 2389: 2385: 2381: 2377: 2373: 2368: 2364: 2360: 2356: 2353: =  2352: 2348: 2344: 2340: 2335: 2331: 2328: 2323: 2319: 2315: 2311: 2310:nondegenerate 2307: 2303: 2299: 2295: 2292: 2288: 2285: 2281: 2273: 2271: 2269: 2265: 2261: 2257: 2254: 2253:real-analytic 2250: 2244: 2227: 2224: 2219: 2198: 2172: 2166: 2163: 2156: 2153: 2152: 2151: 2147: 2145: 2138: 2134: 2129: 2127: 2120: 2101: 2093: 2088: 2084: 2078: 2070: 2065: 2060: 2056: 2050: 2037: 2032: 2028: 2024: 2019: 2014: 2010: 2004: 1994: 1989: 1985: 1981: 1976: 1971: 1967: 1961: 1951: 1946: 1942: 1938: 1933: 1928: 1925: 1915: 1911: 1904: 1897: 1896: 1895: 1892: 1888: 1884: 1880: 1876: 1872: 1852: 1846: 1843: 1840: 1837: 1834: 1828: 1819: 1816: 1813: 1810: 1804: 1798: 1795: 1792: 1789: 1780: 1777: 1771: 1768: 1765: 1759: 1753: 1750: 1747: 1739: 1735: 1727: 1726: 1725: 1711: 1708: 1705: 1702: 1697: 1693: 1684: 1664: 1658: 1655: 1652: 1649: 1646: 1640: 1631: 1628: 1625: 1622: 1616: 1610: 1607: 1604: 1601: 1592: 1589: 1583: 1580: 1577: 1569: 1565: 1561: 1558: 1552: 1549: 1546: 1538: 1534: 1526: 1525: 1524: 1522: 1518: 1514: 1510: 1505: 1503: 1499: 1495: 1491: 1487: 1483: 1480: 1476: 1472: 1468: 1464: 1460: 1456: 1450: 1432: 1424: 1414: 1398: 1395: 1392: 1384: 1374: 1358: 1349: 1345: 1332: 1329: 1321: 1317: 1304: 1297: 1296: 1295: 1273: 1269: 1256: 1253: 1245: 1241: 1228: 1219: 1215: 1202: 1194: 1190: 1177: 1170: 1169: 1168: 1152: 1148: 1144: 1141: 1136: 1132: 1128: 1123: 1119: 1110: 1102: 1086: 1083: 1080: 1067: 1061: 1058: 1055: 1050: 1047: 1044: 1040: 1034: 1031: 1028: 1025: 1022: 1019: 1016: 1013: 1010: 1006: 1002: 999: 992: 991: 990: 988: 983: 981: 950: 946: 942: 938: 899: 896: 891: 888: 885: 882: 879: 875: 871: 854: 840: 837: 832: 829: 826: 823: 820: 816: 812: 802: 801: 800: 798: 794: 791:which maps Ω( 790: 787: 783: 778: 774: 769: 764: 762: 759: +  758: 755: =  754: 750: 746: 726: 720: 709: 706: 703: 690: 687: 684: 681: 678: 674: 670: 655: 647: 635: 634: 633: 631: 627: 623: 619: 614: 612: 608: 607: 602: 598: 594: 590: 586: 582: 578: 574: 570: 566: 562: 558: 554: 550: 546: 542: 534: 532: 530: 526: 525:Hopf problem, 522: 518: 514: 510: 506: 502: 498: 494: 490: 486: 481: 479: 461: 458: 455: 452: 449: 445: 441: 436: 433: 429: 420: 402: 399: 396: 393: 390: 386: 382: 379: 374: 371: 367: 358: 354: 350: 346: 338: 336: 334: 328: 324: 316: 312: 306: 302: 298: 291: 287: 282: 279:-rank tensor 274: 269: 267: 263: 259: 254: 248: 242: 234: 228: 224: 220: 215: 211: 207: 202: 200: 196: 180: 177: 171: 168: 165: 162: 155: 152: 151:vector bundle 136: 133: 130: 125: 121: 109: 105: 102: 99: 95: 91: 87: 84: 80: 72: 70: 68: 64: 59: 57: 53: 49: 48:tangent space 45: 41: 37: 33: 19: 3770:Moving frame 3765:Morse theory 3755:Gauge theory 3547:Tensor field 3476:Closed/Exact 3455:Vector field 3423:Distribution 3364:Hypercomplex 3359:Quaternionic 3257: 3096:Vector field 3054:Smooth atlas 2950: 2944: 2918: 2898: 2878:. Springer. 2875: 2831: 2825: 2781: 2775: 2766: 2721: 2715: 2705: 2636: 2618: 2593: 2574: 2565: 2553: 2544: 2540: 2536: 2532: 2531:). Also, if 2528: 2524: 2520: 2512: 2508: 2506: 2501: 2497: 2493: 2489: 2485: 2481: 2477: 2475: 2469: 2464: 2460: 2455: 2451: 2447: 2443: 2437: 2433: 2429: 2425: 2421: 2414: 2410: 2406: 2402: 2398: 2394: 2387: 2383: 2379: 2375: 2371: 2366: 2362: 2358: 2354: 2350: 2346: 2342: 2338: 2333: 2329: 2321: 2317: 2313: 2305: 2301: 2297: 2293: 2286: 2279: 2277: 2267: 2263: 2255: 2248: 2245: 2242: 2148: 2140: 2136: 2132: 2130: 2122: 2116: 1890: 1886: 1882: 1878: 1874: 1870: 1868: 1682: 1680: 1520: 1516: 1512: 1508: 1506: 1501: 1493: 1489: 1485: 1474: 1470: 1466: 1463:neighborhood 1458: 1454: 1453:given point 1451: 1447: 1293: 1106: 987:identity map 984: 948: 944: 940: 936: 914: 796: 792: 788: 781: 776: 772: 766:As with any 765: 760: 756: 752: 748: 744: 742: 629: 615: 610: 605: 600: 596: 593:vector field 591:is called a 588: 584: 580: 576: 572: 568: 564: 560: 552: 548: 544: 540: 538: 524: 512: 504: 500: 492: 488: 482: 477: 418: 356: 352: 348: 344: 342: 326: 322: 314: 310: 300: 296: 289: 285: 280: 270: 261: 257: 252: 246: 240: 232: 226: 222: 218: 213: 209: 205: 203: 198: 103: 101:tensor field 89: 85: 82: 78: 76: 60: 35: 29: 3715:Levi-Civita 3705:Generalized 3677:Connections 3627:Lie algebra 3559:Volume form 3460:Vector flow 3433:Pushforward 3428:Lie bracket 3327:Lie algebra 3292:G-structure 3081:Pushforward 3061:Submanifold 2662:Chern class 2633:pure spinor 2621:Lie bracket 1479:holomorphic 557:eigenspaces 154:isomorphism 32:mathematics 3838:Stratifold 3796:Diffeology 3592:Associated 3393:Symplectic 3378:Riemannian 3307:Hyperbolic 3234:Submersion 3142:Hopf–Rinow 3076:Submersion 3071:Smooth map 2791:1708.01068 2697:References 2602:direct sum 1685:such that 1498:integrable 768:direct sum 529:Heinz Hopf 266:orientable 113:such that 94:linear map 67:Heinz Hopf 3720:Principal 3695:Ehresmann 3652:Subbundle 3642:Principal 3617:Fibration 3597:Cotangent 3469:Covectors 3322:Lie group 3302:Hermitian 3245:manifolds 3214:Immersion 3209:Foliation 3147:Noether's 3132:Frobenius 3127:De Rham's 3122:Darboux's 3013:Manifolds 2848:0003-486X 2808:119297359 2610:subbundle 2598:isotropic 2386:) form a 2213:¯ 2210:∂ 2182:¯ 2179:∂ 2170:∂ 2075:∂ 2071:− 2047:∂ 2025:− 2001:∂ 1982:− 1958:∂ 1905:− 1829:− 1706:− 1641:− 1562:− 1425:μ 1418:¯ 1408:∂ 1404:∂ 1396:− 1385:μ 1378:¯ 1368:∂ 1364:∂ 1350:μ 1342:∂ 1338:∂ 1322:μ 1314:∂ 1310:∂ 1274:μ 1266:∂ 1262:∂ 1257:− 1246:μ 1238:∂ 1234:∂ 1220:μ 1212:∂ 1208:∂ 1195:μ 1187:∂ 1183:∂ 1153:μ 1137:μ 1124:μ 1084:⋯ 1076:¯ 1073:∂ 1065:∂ 1056:∘ 1041:π 1007:∑ 964:¯ 961:∂ 923:∂ 897:∘ 876:π 867:¯ 864:∂ 838:∘ 817:π 810:∂ 697:Ω 675:⨁ 644:Ω 517:octonions 483:The only 476:for even 446:δ 400:− 387:δ 383:− 281:pointwise 268:as well. 245:. But if 175:→ 166:: 134:− 3863:Category 3816:Orbifold 3811:K-theory 3801:Diffiety 3525:Pullback 3339:Oriented 3317:Kenmotsu 3297:Hadamard 3243:Types of 3192:Geodesic 3017:Glossary 2897:(1980). 2874:(2001). 2758:16578639 2647:See also 2612:and its 2587:subspace 2314:TM → T*M 2300:. Since 2278:Suppose 1515:; i.e., 951:)), and 915:so that 751:), with 417:for odd 339:Examples 243:) = (−1) 221: : 50:. Every 46:on each 3760:History 3743:Related 3657:Tangent 3635:)  3615:)  3582:Adjoint 3574:Bundles 3552:density 3450:Torsion 3416:Vectors 3408:Tensors 3391:)  3376:)  3372:,  3370:Pseudo− 3349:Poisson 3282:Finsler 3277:Fibered 3272:Contact 3270:)  3262:Complex 3260:)  3229:Section 2975:0058213 2967:2372495 2864:0088770 2856:1970051 2784:: 1–9. 2726:Bibcode 2547:) is a 939:,  795:) to Ω( 780:from Ω( 632:-forms 624:of the 620:out of 485:spheres 193:on the 3725:Vector 3710:Koszul 3690:Cartan 3685:Affine 3667:Vector 3662:Tensor 3647:Spinor 3637:Normal 3633:Stable 3587:Affine 3491:bundle 3443:bundle 3389:Almost 3312:Kähler 3268:Almost 3258:Almost 3252:Closed 3152:Sard's 3108:(list) 2973:  2965:  2925:  2905:  2882:  2862:  2854:  2846:  2806:  2756:  2749:224368 2746:  2515:is an 2262:; for 1500:'. If 1107:Every 527:after 277:(1, 1) 111:(1, 1) 108:degree 98:smooth 3833:Sheaf 3607:Fiber 3383:Rizza 3354:Prime 3185:Local 3175:Curve 3037:Atlas 2963:JSTOR 2852:JSTOR 2804:S2CID 2786:arXiv 2639:is a 2635:then 2450:) = ( 1482:atlas 567:and − 555:(the 547:into 239:(det 237:then 38:is a 34:, an 3700:Form 3602:Dual 3535:flow 3398:Tame 3374:Sub− 3287:Flat 3167:Maps 2923:ISBN 2903:ISBN 2880:ISBN 2844:ISSN 2754:PMID 2581:and 2500:has 2488:(•, 2480:and 2428:) = 2405:) = 2308:are 2304:and 2289:, a 2131:The 1881:and 1873:and 1484:for 947:+1, 583:and 551:and 491:and 309:GL(2 293:= −1 251:det 235:= −1 77:Let 65:and 3622:Jet 2955:doi 2836:doi 2796:doi 2744:PMC 2734:doi 2472:)). 1683:A=J 1465:of 559:of 359:): 355:≤ 2 321:GL( 319:to 212:is 204:If 106:of 88:on 30:In 3865:: 3613:Co 2971:MR 2969:. 2961:. 2951:75 2949:. 2939:; 2860:MR 2858:. 2850:. 2842:. 2832:65 2802:. 2794:. 2782:57 2780:. 2752:. 2742:. 2732:. 2722:55 2720:. 2714:. 2643:. 2594:TM 2558:. 2551:. 2543:, 2539:, 2529:Jv 2527:, 2459:)( 2436:, 2434:Ju 2424:, 2420:ω( 2415:Jv 2413:, 2401:, 2382:, 2378:, 2228:0. 1724:, 1492:. 982:. 763:. 597:TM 589:TM 585:TM 581:TM 577:TM 531:. 480:. 421:, 351:, 325:, 313:, 227:TM 225:→ 223:TM 201:. 58:. 3631:( 3611:( 3387:( 3368:( 3266:( 3256:( 3019:) 3015:( 3005:e 2998:t 2991:v 2977:. 2957:: 2931:. 2911:. 2888:. 2866:. 2838:: 2810:. 2798:: 2788:: 2760:. 2736:: 2728:: 2637:M 2575:M 2545:J 2541:ω 2537:M 2533:J 2525:u 2523:( 2521:ω 2513:J 2509:ω 2498:ω 2494:M 2490:J 2486:ω 2482:J 2478:ω 2470:u 2468:( 2465:ω 2461:φ 2456:g 2452:φ 2448:u 2446:( 2444:J 2440:) 2438:v 2432:( 2430:g 2426:v 2422:u 2417:) 2411:u 2409:( 2407:ω 2403:v 2399:u 2397:( 2395:g 2384:J 2380:ω 2376:g 2372:g 2367:g 2363:φ 2359:u 2357:( 2355:ω 2351:ω 2347:u 2343:i 2339:u 2337:( 2334:ω 2330:φ 2322:ω 2318:φ 2306:g 2302:ω 2298:J 2294:g 2287:ω 2280:M 2268:J 2264:C 2256:J 2249:S 2225:= 2220:2 2173:+ 2167:= 2164:d 2143:J 2141:N 2137:J 2125:A 2123:N 2102:. 2099:) 2094:m 2089:i 2085:A 2079:j 2066:m 2061:j 2057:A 2051:i 2043:( 2038:k 2033:m 2029:A 2020:k 2015:i 2011:A 2005:m 1995:m 1990:j 1986:A 1977:k 1972:j 1968:A 1962:m 1952:m 1947:i 1943:A 1939:= 1934:k 1929:j 1926:i 1922:) 1916:A 1912:N 1908:( 1891:A 1887:N 1883:Y 1879:X 1875:Y 1871:X 1853:. 1850:] 1847:Y 1844:J 1841:, 1838:X 1835:J 1832:[ 1826:) 1823:] 1820:Y 1817:J 1814:, 1811:X 1808:[ 1805:+ 1802:] 1799:Y 1796:, 1793:X 1790:J 1787:[ 1784:( 1781:J 1778:+ 1775:] 1772:Y 1769:, 1766:X 1763:[ 1760:= 1757:) 1754:Y 1751:, 1748:X 1745:( 1740:J 1736:N 1712:d 1709:I 1703:= 1698:2 1694:J 1665:. 1662:] 1659:Y 1656:A 1653:, 1650:X 1647:A 1644:[ 1638:) 1635:] 1632:Y 1629:A 1626:, 1623:X 1620:[ 1617:+ 1614:] 1611:Y 1608:, 1605:X 1602:A 1599:[ 1596:( 1593:A 1590:+ 1587:] 1584:Y 1581:, 1578:X 1575:[ 1570:2 1566:A 1559:= 1556:) 1553:Y 1550:, 1547:X 1544:( 1539:A 1535:N 1517:A 1513:M 1509:A 1502:J 1494:J 1490:J 1486:M 1475:J 1471:M 1467:p 1459:J 1455:p 1433:. 1415:z 1399:i 1393:= 1375:z 1359:J 1346:z 1333:i 1330:= 1318:z 1305:J 1270:x 1254:= 1242:y 1229:J 1216:y 1203:= 1191:x 1178:J 1149:y 1145:i 1142:+ 1133:x 1129:= 1120:z 1087:. 1081:+ 1068:+ 1062:= 1059:d 1051:s 1048:, 1045:r 1035:1 1032:+ 1029:q 1026:+ 1023:p 1020:= 1017:s 1014:+ 1011:r 1003:= 1000:d 949:q 945:p 941:q 937:p 900:d 892:1 889:+ 886:q 883:, 880:p 872:= 841:d 833:q 830:, 827:1 824:+ 821:p 813:= 797:M 793:M 789:d 782:M 777:q 775:, 773:p 761:q 757:p 753:r 749:M 745:M 727:. 724:) 721:M 718:( 713:) 710:q 707:, 704:p 701:( 691:r 688:= 685:q 682:+ 679:p 671:= 665:C 660:) 656:M 653:( 648:r 630:r 611:i 606:i 601:J 573:M 569:i 565:i 561:J 553:V 549:V 545:V 541:V 513:S 505:S 501:S 495:( 493:S 489:S 478:i 462:1 459:+ 456:j 453:, 450:i 442:= 437:j 434:i 430:J 419:i 403:1 397:j 394:, 391:i 380:= 375:j 372:i 368:J 357:n 353:j 349:i 345:R 329:) 327:C 323:n 317:) 315:R 311:n 301:M 297:p 290:p 286:J 262:M 258:n 253:J 247:M 241:J 233:J 219:J 214:n 210:M 206:M 181:M 178:T 172:M 169:T 163:J 137:1 131:= 126:2 122:J 104:J 90:M 86:J 79:M 20:)

Index

Almost-complex structure
mathematics
smooth manifold
linear complex structure
tangent space
complex manifold
symplectic geometry
Charles Ehresmann
Heinz Hopf
linear map
smooth
tensor field
degree
vector bundle
isomorphism
tangent bundle
orientable
linear algebra
reduction of the structure group
algebraic topological
spheres
Borel & Serre (1953)
Riemann sphere
octonions
complex structure
Heinz Hopf
eigenspaces
vector field
i
differential forms

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