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4212: 3995: 4233: 4201: 4270: 4243: 4223: 2646:. In other words, if you are "outside" a closed set, you may move a small amount in any direction and still stay outside the set. This is also true if the boundary is the empty set, e.g. in the metric space of rational numbers, for the set of numbers of which the square is less than 2000: 973: 458: 1835: 2747: 844: 540: 1694: 1750: 1572: 390: 246: 3232: 3148: 2886: 2245: 2079: 3368: 3318: 2789: 2026: 1472: 1399: 1333: 922: 805: 416: 327: 179: 3669: 3614: 1005: 2861: 211: 147: 3403: 1916: 2196: 1146: 3270: 2809: 2306: 2150: 2274: 1925: 3637: 3466: 2980: 2933: 2664: 2598: 2394: 1878: 1615: 1446: 1303: 1256: 1209: 1112: 735: 692: 657: 354: 293: 3579: 3559: 3443: 3423: 3192: 3172: 3000: 2953: 2910: 2829: 2767: 2719: 2618: 2575: 2555: 2535: 2511: 2488: 2468: 2434: 2414: 2371: 2216: 2170: 2118: 2098: 2050: 1855: 1790: 1770: 1714: 1655: 1635: 1592: 1536: 1516: 1492: 1419: 1373: 1353: 1276: 1229: 1186: 1166: 1089: 1069: 1049: 1029: 884: 864: 775: 755: 712: 634: 610: 590: 570: 498: 478: 266: 112: 3108: 3060: 4273: 3759: 2444:
Hausdorff space into a compact Hausdorff space, may be described as adjoining limits of certain nonconvergent nets to the space.
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Furthermore, every closed subset of a compact space is compact, and every compact subspace of a Hausdorff space is closed.
671:, which are more general than topological spaces. Notice that this characterization also depends on the surrounding space 421: 3907: 2437: 1795: 4261: 4256: 3744: 3712: 667:, instead of all nets. One value of this characterization is that it may be used as a definition in the context of 2724: 810: 4251: 503: 1660: 1719: 1541: 359: 4153: 216: 3507: 3327:
is an unusual closed set in the sense that it consists entirely of boundary points and is nowhere dense.
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of any family of closed sets is closed (this includes intersections of infinitely many closed sets)
2441: 2221: 2055: 3351: 3288: 2772: 2005: 1451: 1378: 1312: 892: 784: 395: 306: 299:. Yet another equivalent definition is that a set is closed if and only if it contains all of its 158: 4246: 4232: 3642: 3587: 2328: 978: 55: 28: 4181: 4102: 3979: 3967: 3940: 3900: 3238: 3068: 3028: 2834: 184: 120: 4176: 3376: 1889: 4023: 3950: 1995:{\displaystyle f\left(\operatorname {cl} _{X}A\right)\subseteq \operatorname {cl} _{Y}(f(A))} 660: 75: 71: 24: 2175: 1125: 4171: 4123: 4097: 3945: 3582: 3513: 3243: 2794: 2621: 2279: 2123: 1232: 887: 2250: 8: 4018: 2643: 1919: 613: 300: 79: 4222: 3619: 3486: – A function that sends open (resp. closed) subsets to open (resp. closed) subsets 3448: 2962: 2915: 2649: 2580: 2376: 1860: 1597: 1428: 1285: 1238: 1191: 1094: 717: 674: 639: 336: 275: 4216: 4186: 4166: 4087: 4077: 3955: 3935: 3860: 3564: 3544: 3522: 3428: 3408: 3177: 3157: 2985: 2938: 2895: 2889: 2814: 2752: 2704: 2677: 2603: 2560: 2540: 2520: 2514: 2496: 2473: 2453: 2419: 2399: 2356: 2201: 2155: 2103: 2083: 2035: 1840: 1775: 1755: 1699: 1640: 1620: 1577: 1521: 1501: 1477: 1404: 1358: 1338: 1261: 1214: 1171: 1151: 1074: 1054: 1034: 1014: 869: 849: 760: 740: 697: 619: 595: 575: 555: 483: 463: 330: 269: 251: 97: 3081: 3033: 4211: 4204: 4070: 4028: 3893: 3874: 3864: 3837: 3827: 3807: 3797: 3777: 3767: 3740: 3708: 3697: 3283: 2320: 1008: 668: 549: 115: 63: 51: 4236: 2450:
Closed sets also give a useful characterization of compactness: a topological space
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Whether a set is closed depends on the space in which it is embedded. However, the
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with empty intersection admits a finite subcollection with empty intersection.
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a subset is closed if and only if it contains every point that is close to it.
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this terminology allows for a plain English description of closed subsets:
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can be constructed as the intersection of all of these closed supersets.
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is compact if and only if every collection of nonempty closed subsets of
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have the properties listed above, then there exists a unique topology
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Equivalently, a set is closed if and only if it contains all of its
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Some sets are neither open nor closed, for instance the half-open
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for an explanation of the bracket and parenthesis set notation.)
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An alternative characterization of closed sets is available via
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for some (or equivalently, for every) topological super-space
66:, a closed set can be defined as a set which contains all its 2353:", in the sense that, if you embed a compact Hausdorff space 3370:
is an infinite and unbounded closed set in the real numbers.
3194:(inclusive) is closed in the space of rational numbers, but 3885: 3110:
is closed in the metric space of real numbers, and the set
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is continuous if and only if preimages of closed sets in
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The intersection property also allows one to define the
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968:{\displaystyle x\in \operatorname {cl} _{A\cup \{x\}}A} 3330:
Singleton points (and thus finite sets) are closed in
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The notion of closed set is defined above in terms of
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because whether or not a sequence or net converges in
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New Jersey: World Scientific Publishing Company. 3696: 3663: 3631: 3608: 3573: 3553: 3460: 3437: 3417: 3397: 3362: 3312: 3275:Some sets are both open and closed and are called 3264: 3226: 3186: 3166: 3142: 3102: 3054: 2994: 2974: 2947: 2935:which is defined as the smallest closed subset of 2927: 2904: 2880: 2855: 2823: 2803: 2783: 2761: 2741: 2713: 2658: 2612: 2592: 2569: 2549: 2529: 2505: 2482: 2462: 2428: 2408: 2388: 2365: 2300: 2268: 2239: 2210: 2190: 2164: 2144: 2112: 2092: 2073: 2044: 2020: 1994: 1910: 1872: 1849: 1829: 1784: 1764: 1744: 1708: 1688: 1649: 1629: 1609: 1586: 1566: 1530: 1510: 1486: 1466: 1440: 1425:be closed in the "larger" surrounding super-space 1413: 1393: 1367: 1347: 1327: 1297: 1270: 1250: 1223: 1203: 1180: 1160: 1140: 1106: 1083: 1063: 1043: 1023: 999: 967: 916: 878: 858: 838: 799: 769: 749: 729: 706: 686: 651: 628: 604: 584: 564: 534: 492: 472: 452: 410: 384: 348: 321: 287: 260: 240: 205: 173: 141: 106: 1168:if and only if there exists some net (valued) in 4286: 2517:if there exist disjoint, nonempty, open subsets 2436:; the "surrounding space" does not matter here. 1830:{\displaystyle A=X\cap \operatorname {cl} _{Y}A} 82:operation. This should not be confused with a 3405:is a function between topological spaces then 2052:is continuous if and only if for every subset 3901: 3758: 3616:and not on the whole surrounding space (e.g. 3005:Sets that can be constructed as the union of 2742:{\displaystyle \mathbb {F} \neq \varnothing } 1882:Closed sets can also be used to characterize 839:{\displaystyle x\in \operatorname {cl} _{X}A} 3658: 3652: 3603: 3597: 3480: – Subset which is both open and closed 1375:), which is how it is possible for a subset 994: 988: 954: 948: 908: 902: 3504: – Basic subset of a topological space 1538:is always a (potentially proper) subset of 535:{\displaystyle A=\operatorname {cl} _{X}A.} 23:. For a set closed under an operation, see 19:This article is about the complement of an 4269: 4242: 3908: 3894: 1689:{\displaystyle A=\operatorname {cl} _{X}A} 3818: 3510: – Open set containing a given point 3356: 3220: 3136: 2871: 2777: 2729: 2310: 1745:{\displaystyle \operatorname {cl} _{Y}A.} 1696:), it is nevertheless still possible for 1567:{\displaystyle \operatorname {cl} _{Y}A,} 385:{\displaystyle \operatorname {cl} _{X}A;} 89: 3824:Handbook of Analysis and Its Foundations 3788: 3848: 3727: 4287: 3018:sets. These sets need not be closed. 2863:are exactly those sets that belong to 714:depends on what points are present in 241:{\displaystyle X\setminus A\in \tau .} 3889: 3691: 2172:is continuous at a fixed given point 1122:In terms of net convergence, a point 3764:Convergence Foundations Of Topology 3699:Principles of Mathematical Analysis 13: 3304: 3234:is not closed in the real numbers. 2416:will always be a closed subset of 268:if and only if it is equal to its 14: 4306: 3826:. San Diego, CA: Academic Press. 3227:{\displaystyle \cap \mathbb {Q} } 3143:{\displaystyle \cap \mathbb {Q} } 2736: 2319:, a concept that makes sense for 1319: 1071:is thus the set of all points in 223: 165: 74:, a closed set is a set which is 4268: 4241: 4231: 4221: 4210: 4200: 4199: 3993: 2831:such that the closed subsets of 2373:in an arbitrary Hausdorff space 1235:of some other topological space 3721: 3685: 3639:or any other space containing 3541:In particular, whether or not 3535: 3389: 3307: 3292: 3259: 3247: 3213: 3201: 3129: 3117: 3097: 3085: 3049: 3037: 2850: 2838: 2642:A closed set contains its own 2292: 2286: 2263: 2257: 2136: 2130: 2100:maps points that are close to 1989: 1986: 1980: 1974: 1902: 1657:(which happens if and only if 200: 188: 136: 124: 1: 3678: 3009:many closed sets are denoted 2982:Specifically, the closure of 2881:{\displaystyle \mathbb {F} .} 2631: 2240:{\displaystyle A\subseteq X,} 2074:{\displaystyle A\subseteq X,} 1574:which denotes the closure of 3915: 3363:{\displaystyle \mathbb {Z} } 3313:{\displaystyle [1,+\infty )} 2784:{\displaystyle \mathbb {F} } 2120:to points that are close to 2021:{\displaystyle A\subseteq X} 1467:{\displaystyle A\subseteq X} 1394:{\displaystyle A\subseteq X} 1355:(although not an element of 1328:{\displaystyle Y\setminus X} 1031:). Because the closure of 917:{\displaystyle A\cup \{x\},} 800:{\displaystyle A\subseteq X} 616:of every net of elements of 411:{\displaystyle A\subseteq X} 322:{\displaystyle A\subseteq X} 174:{\displaystyle X\setminus A} 16:Complement of an open subset 7: 3796:. Boston: Allyn and Bacon. 3762:; Mynard, Frédéric (2016). 3671:as a topological subspace). 3664:{\displaystyle A\cup \{x\}} 3609:{\displaystyle A\cup \{x\}} 3471: 3021: 2628:consisting of closed sets. 2438:Stone–Čech compactification 1498:topological super-space of 1000:{\displaystyle A\cup \{x\}} 329:is always contained in its 10: 4311: 4162:Banach fixed-point theorem 3849:Willard, Stephen (2004) . 2769:such that the elements of 2635: 2028:; this can be reworded in 866:belongs to the closure of 42:, and related branches of 18: 4195: 4152: 4116: 4002: 3991: 3923: 2856:{\displaystyle (X,\tau )} 2638:Kuratowski closure axioms 2440:, a process that turns a 1716:to be a proper subset of 206:{\displaystyle (X,\tau )} 142:{\displaystyle (X,\tau )} 3528: 3398:{\displaystyle f:X\to Y} 2701:In fact, if given a set 2697:The whole set is closed. 2329:differentiable manifolds 2198:if and only if whenever 1911:{\displaystyle f:X\to Y} 94:By definition, a subset 1280:topological super-space 572:of a topological space 29:Closed (disambiguation) 4217:Mathematics portal 4117:Metrics and properties 4103:Second-countable space 3665: 3633: 3610: 3575: 3555: 3462: 3439: 3419: 3399: 3364: 3314: 3266: 3228: 3188: 3168: 3144: 3104: 3069:Interval (mathematics) 3056: 2996: 2976: 2949: 2929: 2906: 2882: 2857: 2825: 2805: 2785: 2763: 2743: 2715: 2687:closed sets is closed. 2660: 2614: 2594: 2571: 2551: 2531: 2507: 2484: 2464: 2430: 2410: 2390: 2367: 2311:More about closed sets 2302: 2270: 2241: 2212: 2192: 2191:{\displaystyle x\in X} 2166: 2146: 2114: 2094: 2075: 2046: 2022: 1996: 1912: 1874: 1851: 1831: 1786: 1772:is a closed subset of 1766: 1746: 1710: 1690: 1651: 1637:is a closed subset of 1631: 1611: 1588: 1568: 1532: 1512: 1488: 1468: 1442: 1415: 1395: 1369: 1349: 1329: 1299: 1272: 1252: 1225: 1205: 1182: 1162: 1142: 1141:{\displaystyle x\in X} 1108: 1085: 1065: 1045: 1025: 1001: 969: 918: 880: 860: 840: 801: 771: 751: 731: 708: 688: 653: 630: 606: 586: 566: 536: 494: 480:is a closed subset of 474: 454: 412: 386: 350: 323: 289: 262: 242: 207: 175: 143: 108: 90:Equivalent definitions 27:. For other uses, see 3666: 3634: 3611: 3576: 3556: 3463: 3440: 3420: 3400: 3365: 3315: 3267: 3265:{\displaystyle [0,1)} 3229: 3189: 3169: 3145: 3105: 3057: 2997: 2977: 2950: 2930: 2907: 2883: 2858: 2826: 2806: 2804:{\displaystyle \tau } 2786: 2764: 2744: 2716: 2661: 2615: 2595: 2572: 2552: 2532: 2508: 2485: 2465: 2431: 2411: 2391: 2368: 2303: 2301:{\displaystyle f(A).} 2271: 2242: 2218:is close to a subset 2213: 2193: 2167: 2147: 2145:{\displaystyle f(A).} 2115: 2095: 2076: 2047: 2023: 1997: 1913: 1875: 1852: 1832: 1787: 1767: 1747: 1711: 1691: 1652: 1632: 1612: 1589: 1569: 1533: 1513: 1489: 1469: 1443: 1416: 1396: 1370: 1350: 1330: 1300: 1273: 1253: 1226: 1206: 1183: 1163: 1148:is close to a subset 1143: 1109: 1086: 1066: 1046: 1026: 1002: 970: 919: 881: 861: 846:(or equivalently, if 841: 802: 772: 752: 732: 709: 689: 661:first-countable space 654: 631: 612:if and only if every 607: 587: 567: 537: 495: 475: 455: 413: 387: 351: 331:(topological) closure 324: 290: 263: 243: 208: 181:is an open subset of 176: 144: 109: 72:complete metric space 25:closure (mathematics) 4172:Invariance of domain 4124:Euler characteristic 4098:Bundle (mathematics) 3643: 3620: 3588: 3581:depends only on the 3565: 3545: 3514:Region (mathematics) 3449: 3429: 3409: 3377: 3352: 3289: 3272:in the real numbers. 3244: 3198: 3178: 3158: 3114: 3082: 3034: 2986: 2963: 2939: 2916: 2896: 2867: 2835: 2815: 2795: 2773: 2753: 2725: 2705: 2650: 2622:totally disconnected 2604: 2581: 2561: 2541: 2521: 2497: 2493:A topological space 2474: 2454: 2420: 2400: 2377: 2357: 2280: 2269:{\displaystyle f(x)} 2251: 2222: 2202: 2176: 2156: 2124: 2104: 2084: 2056: 2036: 2006: 1926: 1890: 1884:continuous functions 1861: 1841: 1796: 1776: 1756: 1720: 1700: 1661: 1641: 1621: 1598: 1578: 1542: 1522: 1502: 1478: 1452: 1429: 1405: 1379: 1359: 1339: 1313: 1309:exist some point in 1286: 1262: 1239: 1233:topological subspace 1215: 1192: 1172: 1152: 1126: 1095: 1075: 1055: 1035: 1015: 1007:is endowed with the 979: 928: 893: 888:topological subspace 870: 850: 811: 785: 761: 741: 718: 698: 675: 640: 620: 596: 576: 556: 504: 484: 464: 422: 396: 360: 356:which is denoted by 337: 307: 276: 252: 217: 185: 159: 121: 98: 4182:Tychonoff's theorem 4177:Poincaré conjecture 3931:General (point-set) 248:A set is closed in 4167:De Rham cohomology 4088:Polyhedral complex 4078:Simplicial complex 3861:Dover Publications 3661: 3632:{\displaystyle X,} 3629: 3606: 3571: 3551: 3523:Regular closed set 3461:{\displaystyle X.} 3458: 3435: 3415: 3395: 3360: 3310: 3262: 3224: 3184: 3164: 3140: 3100: 3052: 2992: 2975:{\displaystyle A.} 2972: 2945: 2928:{\displaystyle X,} 2925: 2902: 2878: 2853: 2821: 2801: 2781: 2759: 2739: 2711: 2659:{\displaystyle 2.} 2656: 2610: 2593:{\displaystyle X.} 2590: 2567: 2547: 2527: 2503: 2480: 2460: 2442:completely regular 2426: 2406: 2389:{\displaystyle X,} 2386: 2363: 2321:topological spaces 2298: 2266: 2237: 2208: 2188: 2162: 2142: 2110: 2090: 2071: 2042: 2018: 1992: 1908: 1873:{\displaystyle X.} 1870: 1847: 1827: 1782: 1762: 1742: 1706: 1686: 1647: 1627: 1610:{\displaystyle Y;} 1607: 1584: 1564: 1528: 1508: 1484: 1464: 1441:{\displaystyle Y.} 1438: 1411: 1391: 1365: 1345: 1325: 1298:{\displaystyle X,} 1295: 1268: 1251:{\displaystyle Y,} 1248: 1221: 1204:{\displaystyle x.} 1201: 1188:that converges to 1178: 1158: 1138: 1107:{\displaystyle A,} 1104: 1091:that are close to 1081: 1061: 1041: 1021: 997: 965: 914: 876: 856: 836: 797: 767: 747: 730:{\displaystyle X.} 727: 704: 687:{\displaystyle X,} 684: 669:convergence spaces 652:{\displaystyle A.} 649: 626: 602: 582: 562: 532: 490: 470: 450: 408: 382: 349:{\displaystyle X,} 346: 319: 288:{\displaystyle X.} 285: 258: 238: 203: 171: 155:if its complement 139: 104: 4282: 4281: 4071:fundamental group 3870:978-0-486-43479-7 3833:978-0-12-622760-4 3803:978-0-697-06889-7 3773:978-981-4571-52-4 3729:Munkres, James R. 3574:{\displaystyle A} 3554:{\displaystyle x} 3438:{\displaystyle Y} 3418:{\displaystyle f} 3187:{\displaystyle 1} 3167:{\displaystyle 0} 2995:{\displaystyle X} 2948:{\displaystyle X} 2905:{\displaystyle A} 2824:{\displaystyle X} 2762:{\displaystyle X} 2721:and a collection 2714:{\displaystyle X} 2613:{\displaystyle X} 2570:{\displaystyle X} 2550:{\displaystyle B} 2530:{\displaystyle A} 2506:{\displaystyle X} 2483:{\displaystyle X} 2463:{\displaystyle X} 2429:{\displaystyle X} 2409:{\displaystyle D} 2366:{\displaystyle D} 2351:absolutely closed 2211:{\displaystyle x} 2165:{\displaystyle f} 2113:{\displaystyle A} 2093:{\displaystyle f} 2045:{\displaystyle f} 2002:for every subset 1850:{\displaystyle Y} 1785:{\displaystyle X} 1765:{\displaystyle A} 1709:{\displaystyle A} 1650:{\displaystyle X} 1630:{\displaystyle A} 1587:{\displaystyle A} 1531:{\displaystyle A} 1511:{\displaystyle X} 1487:{\displaystyle Y} 1414:{\displaystyle X} 1368:{\displaystyle X} 1348:{\displaystyle A} 1335:that is close to 1271:{\displaystyle Y} 1224:{\displaystyle X} 1181:{\displaystyle A} 1161:{\displaystyle A} 1084:{\displaystyle X} 1064:{\displaystyle X} 1044:{\displaystyle A} 1024:{\displaystyle X} 1011:induced on it by 1009:subspace topology 879:{\displaystyle A} 859:{\displaystyle x} 770:{\displaystyle X} 750:{\displaystyle x} 707:{\displaystyle X} 629:{\displaystyle A} 605:{\displaystyle X} 585:{\displaystyle X} 565:{\displaystyle A} 493:{\displaystyle X} 473:{\displaystyle A} 261:{\displaystyle X} 116:topological space 107:{\displaystyle A} 64:topological space 4302: 4295:General topology 4272: 4271: 4245: 4244: 4235: 4225: 4215: 4214: 4203: 4202: 3997: 3910: 3903: 3896: 3887: 3886: 3882: 3852:General Topology 3845: 3815: 3785: 3751: 3750: 3735:(2nd ed.). 3725: 3719: 3718: 3702: 3689: 3672: 3670: 3668: 3667: 3662: 3638: 3636: 3635: 3630: 3615: 3613: 3612: 3607: 3580: 3578: 3577: 3572: 3560: 3558: 3557: 3552: 3539: 3519: 3498: 3489: 3467: 3465: 3464: 3459: 3444: 3442: 3441: 3436: 3424: 3422: 3421: 3416: 3404: 3402: 3401: 3396: 3369: 3367: 3366: 3361: 3359: 3340:Hausdorff spaces 3319: 3317: 3316: 3311: 3271: 3269: 3268: 3263: 3233: 3231: 3230: 3225: 3223: 3193: 3191: 3190: 3185: 3173: 3171: 3170: 3165: 3152:rational numbers 3149: 3147: 3146: 3141: 3139: 3109: 3107: 3106: 3103:{\displaystyle } 3101: 3066:is closed. (See 3061: 3059: 3058: 3055:{\displaystyle } 3053: 3001: 2999: 2998: 2993: 2981: 2979: 2978: 2973: 2954: 2952: 2951: 2946: 2934: 2932: 2931: 2926: 2911: 2909: 2908: 2903: 2887: 2885: 2884: 2879: 2874: 2862: 2860: 2859: 2854: 2830: 2828: 2827: 2822: 2810: 2808: 2807: 2802: 2790: 2788: 2787: 2782: 2780: 2768: 2766: 2765: 2760: 2748: 2746: 2745: 2740: 2732: 2720: 2718: 2717: 2712: 2665: 2663: 2662: 2657: 2619: 2617: 2616: 2611: 2599: 2597: 2596: 2591: 2576: 2574: 2573: 2568: 2556: 2554: 2553: 2548: 2536: 2534: 2533: 2528: 2512: 2510: 2509: 2504: 2489: 2487: 2486: 2481: 2469: 2467: 2466: 2461: 2435: 2433: 2432: 2427: 2415: 2413: 2412: 2407: 2395: 2393: 2392: 2387: 2372: 2370: 2369: 2364: 2347:Hausdorff spaces 2307: 2305: 2304: 2299: 2275: 2273: 2272: 2267: 2246: 2244: 2243: 2238: 2217: 2215: 2214: 2209: 2197: 2195: 2194: 2189: 2171: 2169: 2168: 2163: 2151: 2149: 2148: 2143: 2119: 2117: 2116: 2111: 2099: 2097: 2096: 2091: 2080: 2078: 2077: 2072: 2051: 2049: 2048: 2043: 2027: 2025: 2024: 2019: 2001: 1999: 1998: 1993: 1970: 1969: 1957: 1953: 1946: 1945: 1917: 1915: 1914: 1909: 1879: 1877: 1876: 1871: 1856: 1854: 1853: 1848: 1836: 1834: 1833: 1828: 1820: 1819: 1791: 1789: 1788: 1783: 1771: 1769: 1768: 1763: 1751: 1749: 1748: 1743: 1732: 1731: 1715: 1713: 1712: 1707: 1695: 1693: 1692: 1687: 1679: 1678: 1656: 1654: 1653: 1648: 1636: 1634: 1633: 1628: 1617:indeed, even if 1616: 1614: 1613: 1608: 1593: 1591: 1590: 1585: 1573: 1571: 1570: 1565: 1554: 1553: 1537: 1535: 1534: 1529: 1517: 1515: 1514: 1509: 1493: 1491: 1490: 1485: 1473: 1471: 1470: 1465: 1447: 1445: 1444: 1439: 1420: 1418: 1417: 1412: 1401:to be closed in 1400: 1398: 1397: 1392: 1374: 1372: 1371: 1366: 1354: 1352: 1351: 1346: 1334: 1332: 1331: 1326: 1304: 1302: 1301: 1296: 1277: 1275: 1274: 1269: 1257: 1255: 1254: 1249: 1230: 1228: 1227: 1222: 1210: 1208: 1207: 1202: 1187: 1185: 1184: 1179: 1167: 1165: 1164: 1159: 1147: 1145: 1144: 1139: 1113: 1111: 1110: 1105: 1090: 1088: 1087: 1082: 1070: 1068: 1067: 1062: 1050: 1048: 1047: 1042: 1030: 1028: 1027: 1022: 1006: 1004: 1003: 998: 974: 972: 971: 966: 958: 957: 923: 921: 920: 915: 885: 883: 882: 877: 865: 863: 862: 857: 845: 843: 842: 837: 829: 828: 806: 804: 803: 798: 776: 774: 773: 768: 756: 754: 753: 748: 736: 734: 733: 728: 713: 711: 710: 705: 693: 691: 690: 685: 658: 656: 655: 650: 636:also belongs to 635: 633: 632: 627: 611: 609: 608: 603: 591: 589: 588: 583: 571: 569: 568: 563: 541: 539: 538: 533: 522: 521: 499: 497: 496: 491: 479: 477: 476: 471: 459: 457: 456: 451: 440: 439: 417: 415: 414: 409: 391: 389: 388: 383: 372: 371: 355: 353: 352: 347: 328: 326: 325: 320: 303:. Every subset 294: 292: 291: 286: 267: 265: 264: 259: 247: 245: 244: 239: 212: 210: 209: 204: 180: 178: 177: 172: 148: 146: 145: 140: 113: 111: 110: 105: 4310: 4309: 4305: 4304: 4303: 4301: 4300: 4299: 4285: 4284: 4283: 4278: 4209: 4191: 4187:Urysohn's lemma 4148: 4112: 3998: 3989: 3961:low-dimensional 3919: 3914: 3871: 3834: 3820:Schechter, Eric 3804: 3790:Dugundji, James 3774: 3760:Dolecki, Szymon 3755: 3754: 3747: 3726: 3722: 3715: 3690: 3686: 3681: 3676: 3675: 3644: 3641: 3640: 3621: 3618: 3617: 3589: 3586: 3585: 3566: 3563: 3562: 3546: 3543: 3542: 3540: 3536: 3531: 3517: 3496: 3487: 3474: 3450: 3447: 3446: 3430: 3427: 3426: 3410: 3407: 3406: 3378: 3375: 3374: 3355: 3353: 3350: 3349: 3335: 3290: 3287: 3286: 3245: 3242: 3241: 3219: 3199: 3196: 3195: 3179: 3176: 3175: 3159: 3156: 3155: 3135: 3115: 3112: 3111: 3083: 3080: 3079: 3035: 3032: 3031: 3024: 3015: 2987: 2984: 2983: 2964: 2961: 2960: 2940: 2937: 2936: 2917: 2914: 2913: 2897: 2894: 2893: 2870: 2868: 2865: 2864: 2836: 2833: 2832: 2816: 2813: 2812: 2796: 2793: 2792: 2776: 2774: 2771: 2770: 2754: 2751: 2750: 2728: 2726: 2723: 2722: 2706: 2703: 2702: 2651: 2648: 2647: 2640: 2634: 2605: 2602: 2601: 2582: 2579: 2578: 2577:whose union is 2562: 2559: 2558: 2542: 2539: 2538: 2522: 2519: 2518: 2498: 2495: 2494: 2475: 2472: 2471: 2455: 2452: 2451: 2421: 2418: 2417: 2401: 2398: 2397: 2378: 2375: 2374: 2358: 2355: 2354: 2313: 2281: 2278: 2277: 2252: 2249: 2248: 2223: 2220: 2219: 2203: 2200: 2199: 2177: 2174: 2173: 2157: 2154: 2153: 2125: 2122: 2121: 2105: 2102: 2101: 2085: 2082: 2081: 2057: 2054: 2053: 2037: 2034: 2033: 2007: 2004: 2003: 1965: 1961: 1941: 1937: 1936: 1932: 1927: 1924: 1923: 1922:if and only if 1891: 1888: 1887: 1862: 1859: 1858: 1842: 1839: 1838: 1815: 1811: 1797: 1794: 1793: 1792:if and only if 1777: 1774: 1773: 1757: 1754: 1753: 1727: 1723: 1721: 1718: 1717: 1701: 1698: 1697: 1674: 1670: 1662: 1659: 1658: 1642: 1639: 1638: 1622: 1619: 1618: 1599: 1596: 1595: 1579: 1576: 1575: 1549: 1545: 1543: 1540: 1539: 1523: 1520: 1519: 1503: 1500: 1499: 1479: 1476: 1475: 1453: 1450: 1449: 1430: 1427: 1426: 1406: 1403: 1402: 1380: 1377: 1376: 1360: 1357: 1356: 1340: 1337: 1336: 1314: 1311: 1310: 1287: 1284: 1283: 1263: 1260: 1259: 1240: 1237: 1236: 1216: 1213: 1212: 1193: 1190: 1189: 1173: 1170: 1169: 1153: 1150: 1149: 1127: 1124: 1123: 1096: 1093: 1092: 1076: 1073: 1072: 1056: 1053: 1052: 1036: 1033: 1032: 1016: 1013: 1012: 980: 977: 976: 941: 937: 929: 926: 925: 894: 891: 890: 871: 868: 867: 851: 848: 847: 824: 820: 812: 809: 808: 786: 783: 782: 762: 759: 758: 742: 739: 738: 719: 716: 715: 699: 696: 695: 676: 673: 672: 641: 638: 637: 621: 618: 617: 597: 594: 593: 577: 574: 573: 557: 554: 553: 517: 513: 505: 502: 501: 500:if and only if 485: 482: 481: 465: 462: 461: 435: 431: 423: 420: 419: 397: 394: 393: 367: 363: 361: 358: 357: 338: 335: 334: 308: 305: 304: 301:boundary points 277: 274: 273: 253: 250: 249: 218: 215: 214: 186: 183: 182: 160: 157: 156: 122: 119: 118: 99: 96: 95: 92: 84:closed manifold 32: 17: 12: 11: 5: 4308: 4298: 4297: 4280: 4279: 4277: 4276: 4266: 4265: 4264: 4259: 4254: 4239: 4229: 4219: 4207: 4196: 4193: 4192: 4190: 4189: 4184: 4179: 4174: 4169: 4164: 4158: 4156: 4150: 4149: 4147: 4146: 4141: 4136: 4134:Winding number 4131: 4126: 4120: 4118: 4114: 4113: 4111: 4110: 4105: 4100: 4095: 4090: 4085: 4080: 4075: 4074: 4073: 4068: 4066:homotopy group 4058: 4057: 4056: 4051: 4046: 4041: 4036: 4026: 4021: 4016: 4006: 4004: 4000: 3999: 3992: 3990: 3988: 3987: 3982: 3977: 3976: 3975: 3965: 3964: 3963: 3953: 3948: 3943: 3938: 3933: 3927: 3925: 3921: 3920: 3913: 3912: 3905: 3898: 3890: 3884: 3883: 3869: 3846: 3832: 3816: 3802: 3786: 3772: 3753: 3752: 3745: 3720: 3713: 3683: 3682: 3680: 3677: 3674: 3673: 3660: 3657: 3654: 3651: 3648: 3628: 3625: 3605: 3602: 3599: 3596: 3593: 3570: 3550: 3533: 3532: 3530: 3527: 3526: 3525: 3520: 3511: 3505: 3499: 3490: 3481: 3473: 3470: 3469: 3468: 3457: 3454: 3445:are closed in 3434: 3414: 3394: 3391: 3388: 3385: 3382: 3371: 3358: 3343: 3333: 3328: 3321: 3309: 3306: 3303: 3300: 3297: 3294: 3280: 3273: 3261: 3258: 3255: 3252: 3249: 3235: 3222: 3218: 3215: 3212: 3209: 3206: 3203: 3183: 3163: 3138: 3134: 3131: 3128: 3125: 3122: 3119: 3099: 3096: 3093: 3090: 3087: 3073: 3071: 3051: 3048: 3045: 3042: 3039: 3023: 3020: 3013: 2991: 2971: 2968: 2944: 2924: 2921: 2901: 2877: 2873: 2852: 2849: 2846: 2843: 2840: 2820: 2800: 2779: 2758: 2749:of subsets of 2738: 2735: 2731: 2710: 2699: 2698: 2695: 2688: 2686: 2674: 2655: 2633: 2630: 2609: 2589: 2586: 2566: 2546: 2526: 2502: 2479: 2459: 2425: 2405: 2385: 2382: 2362: 2333:uniform spaces 2312: 2309: 2297: 2294: 2291: 2288: 2285: 2265: 2262: 2259: 2256: 2236: 2233: 2230: 2227: 2207: 2187: 2184: 2181: 2161: 2141: 2138: 2135: 2132: 2129: 2109: 2089: 2070: 2067: 2064: 2061: 2041: 2017: 2014: 2011: 1991: 1988: 1985: 1982: 1979: 1976: 1973: 1968: 1964: 1960: 1956: 1952: 1949: 1944: 1940: 1935: 1931: 1907: 1904: 1901: 1898: 1895: 1869: 1866: 1846: 1826: 1823: 1818: 1814: 1810: 1807: 1804: 1801: 1781: 1761: 1741: 1738: 1735: 1730: 1726: 1705: 1685: 1682: 1677: 1673: 1669: 1666: 1646: 1626: 1606: 1603: 1583: 1563: 1560: 1557: 1552: 1548: 1527: 1507: 1497: 1483: 1463: 1460: 1457: 1437: 1434: 1424: 1410: 1390: 1387: 1384: 1364: 1344: 1324: 1321: 1318: 1308: 1294: 1291: 1281: 1267: 1258:in which case 1247: 1244: 1220: 1200: 1197: 1177: 1157: 1137: 1134: 1131: 1120: 1119: 1103: 1100: 1080: 1060: 1040: 1020: 996: 993: 990: 987: 984: 964: 961: 956: 953: 950: 947: 944: 940: 936: 933: 913: 910: 907: 904: 901: 898: 875: 855: 835: 832: 827: 823: 819: 816: 796: 793: 790: 780: 777:is said to be 766: 746: 726: 723: 703: 683: 680: 648: 645: 625: 601: 581: 561: 531: 528: 525: 520: 516: 512: 509: 489: 469: 449: 446: 443: 438: 434: 430: 427: 407: 404: 401: 381: 378: 375: 370: 366: 345: 342: 318: 315: 312: 284: 281: 257: 237: 234: 231: 228: 225: 222: 213:; that is, if 202: 199: 196: 193: 190: 170: 167: 164: 153: 138: 135: 132: 129: 126: 103: 91: 88: 15: 9: 6: 4: 3: 2: 4307: 4296: 4293: 4292: 4290: 4275: 4267: 4263: 4260: 4258: 4255: 4253: 4250: 4249: 4248: 4240: 4238: 4234: 4230: 4228: 4224: 4220: 4218: 4213: 4208: 4206: 4198: 4197: 4194: 4188: 4185: 4183: 4180: 4178: 4175: 4173: 4170: 4168: 4165: 4163: 4160: 4159: 4157: 4155: 4151: 4145: 4144:Orientability 4142: 4140: 4137: 4135: 4132: 4130: 4127: 4125: 4122: 4121: 4119: 4115: 4109: 4106: 4104: 4101: 4099: 4096: 4094: 4091: 4089: 4086: 4084: 4081: 4079: 4076: 4072: 4069: 4067: 4064: 4063: 4062: 4059: 4055: 4052: 4050: 4047: 4045: 4042: 4040: 4037: 4035: 4032: 4031: 4030: 4027: 4025: 4022: 4020: 4017: 4015: 4011: 4008: 4007: 4005: 4001: 3996: 3986: 3983: 3981: 3980:Set-theoretic 3978: 3974: 3971: 3970: 3969: 3966: 3962: 3959: 3958: 3957: 3954: 3952: 3949: 3947: 3944: 3942: 3941:Combinatorial 3939: 3937: 3934: 3932: 3929: 3928: 3926: 3922: 3918: 3911: 3906: 3904: 3899: 3897: 3892: 3891: 3888: 3880: 3876: 3872: 3866: 3862: 3858: 3857:Mineola, N.Y. 3854: 3853: 3847: 3843: 3839: 3835: 3829: 3825: 3821: 3817: 3813: 3809: 3805: 3799: 3795: 3791: 3787: 3783: 3779: 3775: 3769: 3765: 3761: 3757: 3756: 3748: 3746:0-13-181629-2 3742: 3738: 3737:Prentice Hall 3734: 3730: 3724: 3716: 3714:0-07-054235-X 3710: 3706: 3701: 3700: 3694: 3693:Rudin, Walter 3688: 3684: 3655: 3649: 3646: 3626: 3623: 3600: 3594: 3591: 3584: 3568: 3548: 3538: 3534: 3524: 3521: 3515: 3512: 3509: 3508:Neighbourhood 3506: 3503: 3500: 3494: 3493:Closed region 3491: 3485: 3482: 3479: 3476: 3475: 3455: 3452: 3432: 3412: 3392: 3386: 3383: 3380: 3372: 3348: 3344: 3341: 3337: 3329: 3326: 3322: 3301: 3298: 3295: 3285: 3281: 3278: 3274: 3256: 3253: 3250: 3240: 3236: 3216: 3210: 3207: 3204: 3181: 3161: 3153: 3132: 3126: 3123: 3120: 3094: 3091: 3088: 3078: 3077:unit interval 3074: 3070: 3067: 3065: 3046: 3043: 3040: 3030: 3026: 3025: 3019: 3017: 3016: 3008: 3003: 2989: 2969: 2966: 2958: 2942: 2922: 2919: 2899: 2891: 2875: 2847: 2844: 2841: 2818: 2798: 2756: 2733: 2708: 2696: 2693: 2689: 2684: 2681: 2679: 2675: 2672: 2668: 2667: 2666: 2653: 2645: 2639: 2629: 2627: 2624:if it has an 2623: 2607: 2600:Furthermore, 2587: 2584: 2564: 2544: 2524: 2516: 2500: 2491: 2477: 2457: 2448: 2445: 2443: 2439: 2423: 2403: 2383: 2380: 2360: 2352: 2348: 2345: 2340: 2338: 2334: 2330: 2326: 2325:metric spaces 2322: 2318: 2308: 2295: 2289: 2283: 2260: 2254: 2234: 2231: 2228: 2225: 2205: 2185: 2182: 2179: 2159: 2139: 2133: 2127: 2107: 2087: 2068: 2065: 2062: 2059: 2039: 2031: 2030:plain English 2015: 2012: 2009: 1983: 1977: 1971: 1966: 1962: 1958: 1954: 1950: 1947: 1942: 1938: 1933: 1929: 1921: 1905: 1899: 1896: 1893: 1885: 1880: 1867: 1864: 1844: 1824: 1821: 1816: 1812: 1808: 1805: 1802: 1799: 1779: 1759: 1739: 1736: 1733: 1728: 1724: 1703: 1683: 1680: 1675: 1671: 1667: 1664: 1644: 1624: 1604: 1601: 1581: 1561: 1558: 1555: 1550: 1546: 1525: 1505: 1495: 1481: 1461: 1458: 1455: 1435: 1432: 1422: 1408: 1388: 1385: 1382: 1362: 1342: 1322: 1316: 1306: 1292: 1289: 1279: 1265: 1245: 1242: 1234: 1218: 1198: 1195: 1175: 1155: 1135: 1132: 1129: 1117: 1116: 1115: 1101: 1098: 1078: 1058: 1038: 1018: 1010: 991: 985: 982: 962: 959: 951: 945: 942: 938: 934: 931: 911: 905: 899: 896: 889: 873: 853: 833: 830: 825: 821: 817: 814: 794: 791: 788: 778: 764: 744: 724: 721: 701: 681: 678: 670: 666: 662: 646: 643: 623: 615: 599: 592:is closed in 579: 559: 551: 547: 542: 529: 526: 523: 518: 514: 510: 507: 487: 467: 447: 444: 441: 436: 432: 428: 425: 405: 402: 399: 379: 376: 373: 368: 364: 343: 340: 332: 316: 313: 310: 302: 298: 282: 279: 271: 255: 235: 232: 229: 226: 220: 197: 194: 191: 168: 162: 154: 151: 133: 130: 127: 117: 101: 87: 85: 81: 77: 73: 69: 65: 61: 57: 53: 49: 45: 41: 37: 30: 26: 22: 4274:Publications 4139:Chern number 4129:Betti number 4013: 4012: / 4003:Key concepts 3951:Differential 3851: 3823: 3793: 3763: 3732: 3723: 3698: 3687: 3561:is close to 3537: 3064:real numbers 3010: 3004: 2700: 2671:intersection 2641: 2515:disconnected 2492: 2449: 2446: 2341: 2337:gauge spaces 2314: 2276:is close to 1881: 1278:is called a 1121: 552:. A subset 543: 392:that is, if 297:limit points 150: 93: 68:limit points 47: 33: 4237:Wikiversity 4154:Key results 3705:McGraw-Hill 3345:The set of 3277:clopen sets 3027:The closed 2912:in a space 2152:Similarly, 1305:then there 44:mathematics 4083:CW complex 4024:Continuity 4014:Closed set 3973:cohomology 3679:References 3484:Closed map 3478:Clopen set 3325:Cantor set 3320:is closed. 2955:that is a 2694:is closed. 2636:See also: 2632:Properties 2626:open basis 1920:continuous 460:Moreover, 149:is called 78:under the 56:complement 48:closed set 4262:geometric 4257:algebraic 4108:Cobordism 4044:Hausdorff 4039:connected 3956:Geometric 3946:Continuum 3936:Algebraic 3842:175294365 3812:395340485 3782:945169917 3650:∪ 3595:∪ 3390:→ 3305:∞ 3217:∩ 3133:∩ 3007:countably 2892:of a set 2848:τ 2799:τ 2737:∅ 2734:≠ 2692:empty set 2317:open sets 2229:⊆ 2183:∈ 2063:⊆ 2013:⊆ 1972:⁡ 1959:⊆ 1948:⁡ 1903:→ 1822:⁡ 1809:∩ 1752:However, 1734:⁡ 1681:⁡ 1556:⁡ 1459:⊆ 1386:⊆ 1320:∖ 1133:∈ 986:∪ 960:⁡ 946:∪ 935:∈ 900:∪ 831:⁡ 818:∈ 792:⊆ 781:a subset 665:sequences 546:sequences 524:⁡ 442:⁡ 429:⊆ 403:⊆ 374:⁡ 314:⊆ 233:τ 230:∈ 224:∖ 198:τ 166:∖ 134:τ 4289:Category 4227:Wikibook 4205:Category 4093:Manifold 4061:Homotopy 4019:Interior 4010:Open set 3968:Homology 3917:Topology 3822:(1996). 3794:Topology 3792:(1966). 3733:Topology 3731:(2000). 3695:(1976). 3583:subspace 3502:Open set 3472:See also 3347:integers 3239:interval 3154:between 3029:interval 3022:Examples 2957:superset 2683:finitely 2644:boundary 1886:: a map 924:meaning 779:close to 737:A point 60:open set 40:topology 36:geometry 21:open set 4252:general 4054:uniform 4034:compact 3985:Digital 2890:closure 2344:compact 1474:and if 1421:but to 886:in the 270:closure 70:. In a 62:. In a 4247:Topics 4049:metric 3924:Fields 3879:115240 3877:  3867:  3840:  3830:  3810:  3800:  3780:  3770:  3743:  3711:  3336:spaces 2335:, and 975:where 152:closed 76:closed 58:is an 54:whose 4029:Space 3529:Notes 2678:union 2396:then 2349:are " 2247:then 1518:then 1307:might 1231:is a 659:In a 614:limit 418:then 114:of a 80:limit 50:is a 3875:OCLC 3865:ISBN 3838:OCLC 3828:ISBN 3808:OCLC 3798:ISBN 3778:OCLC 3768:ISBN 3741:ISBN 3709:ISBN 3338:and 3323:The 3282:The 3174:and 3075:The 2690:The 2685:many 2676:The 2669:Any 2537:and 2032:as: 550:nets 548:and 46:, a 3373:If 3284:ray 3150:of 3062:of 2959:of 2811:on 2680:of 2620:is 2557:of 2513:is 2339:. 1918:is 1857:of 1594:in 1496:any 1494:is 1448:If 1423:not 1282:of 1211:If 1051:in 807:if 757:in 333:in 272:in 52:set 34:In 4291:: 3873:. 3863:. 3859:: 3855:. 3836:. 3806:. 3776:. 3739:. 3707:. 3703:. 2654:2. 2331:, 2327:, 1963:cl 1939:cl 1813:cl 1725:cl 1672:cl 1547:cl 939:cl 822:cl 515:cl 433:cl 365:cl 86:. 38:, 3909:e 3902:t 3895:v 3881:. 3844:. 3814:. 3784:. 3749:. 3717:. 3659:} 3656:x 3653:{ 3647:A 3627:, 3624:X 3604:} 3601:x 3598:{ 3592:A 3569:A 3549:x 3456:. 3453:X 3433:Y 3413:f 3393:Y 3387:X 3384:: 3381:f 3357:Z 3342:. 3334:1 3332:T 3308:) 3302:+ 3299:, 3296:1 3293:[ 3279:. 3260:) 3257:1 3254:, 3251:0 3248:[ 3221:Q 3214:] 3211:1 3208:, 3205:0 3202:[ 3182:1 3162:0 3137:Q 3130:] 3127:1 3124:, 3121:0 3118:[ 3098:] 3095:1 3092:, 3089:0 3086:[ 3050:] 3047:b 3044:, 3041:a 3038:[ 3014:σ 3012:F 2990:X 2970:. 2967:A 2943:X 2923:, 2920:X 2900:A 2876:. 2872:F 2851:) 2845:, 2842:X 2839:( 2819:X 2778:F 2757:X 2730:F 2709:X 2608:X 2588:. 2585:X 2565:X 2545:B 2525:A 2501:X 2478:X 2458:X 2424:X 2404:D 2384:, 2381:X 2361:D 2296:. 2293:) 2290:A 2287:( 2284:f 2264:) 2261:x 2258:( 2255:f 2235:, 2232:X 2226:A 2206:x 2186:X 2180:x 2160:f 2140:. 2137:) 2134:A 2131:( 2128:f 2108:A 2088:f 2069:, 2066:X 2060:A 2040:f 2016:X 2010:A 1990:) 1987:) 1984:A 1981:( 1978:f 1975:( 1967:Y 1955:) 1951:A 1943:X 1934:( 1930:f 1906:Y 1900:X 1897:: 1894:f 1868:. 1865:X 1845:Y 1825:A 1817:Y 1806:X 1803:= 1800:A 1780:X 1760:A 1740:. 1737:A 1729:Y 1704:A 1684:A 1676:X 1668:= 1665:A 1645:X 1625:A 1605:; 1602:Y 1582:A 1562:, 1559:A 1551:Y 1526:A 1506:X 1482:Y 1462:X 1456:A 1436:. 1433:Y 1409:X 1389:X 1383:A 1363:X 1343:A 1323:X 1317:Y 1293:, 1290:X 1266:Y 1246:, 1243:Y 1219:X 1199:. 1196:x 1176:A 1156:A 1136:X 1130:x 1102:, 1099:A 1079:X 1059:X 1039:A 1019:X 995:} 992:x 989:{ 983:A 963:A 955:} 952:x 949:{ 943:A 932:x 912:, 909:} 906:x 903:{ 897:A 874:A 854:x 834:A 826:X 815:x 795:X 789:A 765:X 745:x 725:. 722:X 702:X 682:, 679:X 647:. 644:A 624:A 600:X 580:X 560:A 530:. 527:A 519:X 511:= 508:A 488:X 468:A 448:. 445:A 437:X 426:A 406:X 400:A 380:; 377:A 369:X 344:, 341:X 317:X 311:A 283:. 280:X 256:X 236:. 227:A 221:X 201:) 195:, 192:X 189:( 169:A 163:X 137:) 131:, 128:X 125:( 102:A 31:.

Index

open set
closure (mathematics)
Closed (disambiguation)
geometry
topology
mathematics
set
complement
open set
topological space
limit points
complete metric space
closed
limit
closed manifold
topological space
closure
limit points
boundary points
(topological) closure
sequences
nets
limit
first-countable space
sequences
convergence spaces
topological subspace
subspace topology
topological subspace
continuous functions

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