Knowledge (XXG)

Separation axiom

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if each is disjoint from the other's closure, though the closures themselves do not have to be disjoint. Equivalently, each subset is included in an open set disjoint from the other subset. All of the remaining conditions for separation of sets may also be applied to points (or to a point and a set)
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These conditions are given in order of increasing strength: Any two topologically distinguishable points must be distinct, and any two separated points must be topologically distinguishable. Any two separated sets must be disjoint, any two sets separated by neighbourhoods must be separated, and so
1283:, and one goes from the left side to the right side by removing that requirement, using the Kolmogorov quotient operation. (The names in parentheses given on the left side of this table are generally ambiguous or at least less well known; but they are used in the diagram below.) 567:
Most of these axioms have alternative definitions with the same meaning; the definitions given here fall into a consistent pattern that relates the various notions of separation defined in the previous section. Other possible definitions can be found in the individual articles.
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There are some other conditions on topological spaces that are sometimes classified with the separation axioms, but these don't fit in with the usual separation axioms as completely. Other than their definitions, they aren't discussed here; see their individual articles.
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as follows: "P" = "perfectly", "C" = "completely", "N" = "normal", and "R" (without a subscript) = "regular". A bullet indicates that there is no special name for a space at that spot. The dash at the bottom indicates no condition.
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The following table summarizes the separation axioms as well as the implications between them: cells which are merged represent equivalent properties, each axiom implies the ones in the cells to its left, and if we assume the
351:(in any of various ways). The separation axioms all say, in one way or another, that points or sets that are distinguishable or separated in some weak sense must also be distinguishable or separated in some stronger sense. 250:
An illustration of some of the separation axioms. Grey amorphous broken-outline regions indicate open sets surrounding disjoint closed sets or points: red solid-outline circles denote closed sets while black dots represent
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together imply a host of other properties, since combining the two properties leads through the many nodes on the right-side branch. Since regularity is the most well known of these, spaces that are both normal and
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for more information. When applied to the separation axioms, this leads to the relationships in the table to the left below. In this table, one goes from the right side to the left side by adding the requirement of
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Two properties may be combined using this diagram by following the diagram upwards until both branches meet. For example, if a space is both completely normal ("CN") and completely Hausdorff ("CT
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are often called "normal Hausdorff spaces" by people that wish to avoid the ambiguous "T" notation. These conventions can be generalised to other regular spaces and Hausdorff spaces.
290:, but rather defining properties which may be specified to distinguish certain types of topological spaces. The separation axioms are denoted with the letter "T" after the 378:(or equivalently the same open neighbourhoods); that is, at least one of them has a neighbourhood that is not a neighbourhood of the other (or equivalently there is an 1071:
if any two disjoint closed sets are precisely separated by a continuous function. Every perfectly normal space is also both completely normal and completely regular.
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will be considered separated, by neighbourhoods, by closed neighbourhoods, by a continuous function, precisely by a function, if and only if their singleton sets {
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are separated by neighbourhoods. (In fact, a space is normal if and only if any two disjoint closed sets can be separated by a continuous function; this is
1173: 775: 121: 103: 1551:. More briefly, every irreducible closed set has a unique generic point. Any Hausdorff space must be sober, and any sober space must be T 1872: 1037: 1079: 553: 301: 235: 1286: 287: 1844: 604: 534: 382:
that one point belongs to but the other point does not). That is, at least one of the points does not belong to the other's
1727:(Hausdorff) space satisfies the axiom that all compact subsets are closed, but the reverse is not necessarily true; for the 564:", etc. Many of the concepts also have several names; however, the one listed first is always least likely to be ambiguous. 685:
is Fréchet"; one should avoid saying "Fréchet space" in this context, since there is another entirely different notion of
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because every single-point set is necessarily compact and thus closed, but the reverse is not necessarily true; for the
1459:, the relationships between the separation axioms are indicated in the diagram to the right. In this diagram, the non-T 401:
if each of them has a neighbourhood that is not a neighbourhood of the other; that is, neither belongs to the other's
375: 1916: 1696:. In fact, fully normal spaces actually have more to do with paracompactness than with the usual separation axioms. 1178: 802: 20: 1203: 1183: 900: 1507:
are typically called "normal regular spaces". In a somewhat similar fashion, spaces that are both normal and T
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space (less ambiguously known as a completely normal Hausdorff space, as can be seen in the table above).
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if any two separated sets are separated by neighbourhoods. Every completely normal space is also normal.
607:. (It will be a common theme among the separation axioms to have one version of an axiom that requires T 304:. Especially in older literature, different authors might have different definitions of each condition. 1900: 1728: 1563: 986: 1275: 690: 462: 297:("separation axiom"), and increasing numerical subscripts denote stronger and stronger properties. 1262:
axiom is special in that it can not only be added to a property (so that completely regular plus T
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that is not the (possibly nondisjoint) union of two smaller closed sets, there is a unique point
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and completely regular. Every Tychonoff space is both regular Hausdorff and completely Hausdorff.
402: 383: 34: 975: 1921: 1868: 1840: 1716: 1595: 1238: 924:, they are separated by a continuous function. Every completely regular space is also regular. 576: 317: 312:
Before we define the separation axioms themselves, we give concrete meaning to the concept of
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axiom, then each axiom also implies the ones in the cells above it (for example, all normal T
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many points, the compact sets are all finite and hence all closed but the space is not T
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side of the slash, so a completely normal completely Hausdorff space is the same as a T
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For more on these conditions (including their use outside the separation axioms), see
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points. It's not enough for elements of a topological space to be distinct (that is,
139: 1583:. Any Hausdorff space must be weak Hausdorff, and any weak Hausdorff space must be T 1895: 1468: 1223: 1208: 1017:
and normal. Every normal Hausdorff space is also both Tychonoff and normal regular.
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are separated by a continuous function. Every completely Hausdorff space is also T
1834: 1732: 1693: 1531: 260: 1723:, every subset is compact but not every subset is closed. Furthermore, every T 1266:
is Tychonoff) but also be subtracted from a property (so that Hausdorff minus T
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will also be separated by closed neighbourhoods.) Every regular space is also R
853:, they are separated by neighbourhoods. (In fact, in a regular space, any such 1652: 1101:. Every perfectly normal Hausdorff space is also completely normal Hausdorff. 661:
are separated. Equivalently, every single-point set is a closed set. Thus,
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The separation axioms are about the use of topological means to distinguish
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that one wishes to consider. Some of these restrictions are given by the
256: 67: 1711:(Hausdorff) in strength. A space satisfying this axiom is necessarily T 1680:
and fully normal. Every fully normal space is normal and every fully T
263:, there are several restrictions that one often makes on the kinds of 344: 681:
space", "Fréchet topology", and "suppose that the topological space
1059:. Every completely normal Hausdorff space is also normal Hausdorff. 994:
and normal. Every normal regular space is also completely regular.
1487:(even though completely normal spaces may not be), one takes the T 1463:
version of a condition is on the left side of the slash, and the T
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axioms mentioned in the Main Definitions, with these definitions)
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of a topological space to be disjoint; we may want them to be
1479:"), then following both branches up, one finds the spot "•/T 1285: 438:} are separated according to the corresponding criterion. 560:" are sometimes interchanged, similarly "regular" and "T 554:
alternative meanings in some of mathematical literature
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if they have disjoint closed neighbourhoods. They are
712:, if any two topologically distinguishable points in 630:, if any two topologically distinguishable points in 888:
and regular. Every regular Hausdorff space is also T
1467:version is on the right side. Letters are used for 211: 191: 173: 156: 138: 120: 102: 84: 66: 48: 40: 28: 16:
Axioms in topology defining notions of "separation"
790:are separated by closed neighbourhoods. Every T 453:if they have disjoint neighbourhoods. They are 556:; for example, the meanings of "normal" and "T 1611:. Any regular space must also be semiregular. 1575:from a compact Hausdorff space, the image of 1498:As can be seen from the diagram, normal and R 8: 1901:Table of separation and metrisability axioms 546: 492:precisely separated by a continuous function 1688:. Moreover, one can show that every fully T 1867:. Reading, Mass.: Addison-Wesley Pub. Co. 1483:". Since completely Hausdorff spaces are T 1455:Other than the inclusion or exclusion of T 545:These definitions all use essentially the 282:The separation axioms are not fundamental 1816: 1804: 1792: 1780: 1768: 677:. (Although one may say such things as "T 1836:Handbook of Analysis and its Foundations 1293: 1116: 755:is Hausdorff if and only if it is both T 716:are separated by neighbourhoods. Every R 486:({0}) and B is a subset of the preimage 358:be a topological space. Then two points 1761: 1290:Hasse diagram of the separation axioms. 1055:, if it is both completely normal and T 751:are separated by neighbourhoods. Thus, 302:separation axioms have varied over time 1097:, if it is both perfectly normal and T 970:if any two disjoint closed subsets of 494:if there exists a continuous function 320:. (Separated sets are not the same as 25: 1719:on infinitely many points, which is T 1114:spaces are also completely regular). 571:In all of the following definitions, 374:if they do not have exactly the same 7: 1274:), in a fairly precise sense; see 1128:Separated by closed neighborhoods 459:separated by a continuous function 455:separated by closed neighbourhoods 14: 763:. Every Hausdorff space is also T 343:. Similarly, it's not enough for 19:For the axiom of set theory, see 1254:Relationships between the axioms 1134:Precisely separated by function 813:, if any two distinct points in 786:, if any two distinct points in 747:, if any two distinct points in 657:, if any two distinct points in 599:, if any two distinct points in 422:by using singleton sets. Points 324:, defined in the next section.) 1896:Separation Axioms at ProvenMath 1627:, there is a nonempty open set 479:such that A is a subset of the 300:The precise definitions of the 1701:all compact subsets are closed 1430:Completely normal Hausdorff (T 611:and one version that doesn't.) 535:Topological distinguishability 405:. More generally, two subsets 1: 1839:. San Diego: Academic Press. 1623:if for any nonempty open set 1567:if, for every continuous map 1442:Perfectly normal Hausdorff (T 1190:Closed set and point outside 605:topologically distinguishable 372:topologically distinguishable 341:topologically distinguishable 271:. These are sometimes called 952:completely regular Hausdorff 1125:Separated by neighborhoods 1038:completely normal Hausdorff 669:if and only if it is both T 451:separated by neighbourhoods 273:Tychonoff separation axioms 1938: 1543:such that the closure of { 1437:Completely normal regular 1080:perfectly normal Hausdorff 528: 339:); we may want them to be 21:Axiom schema of separation 18: 1861:Willard, Stephen (1970). 1631:such that the closure of 1535:if, for every closed set 1237: 1222: 1207: 1197: 552:Many of these names have 490:({1}). Finally, they are 231: 1833:Schechter, Eric (1997). 794:space is also Hausdorff. 1517:Other separation axioms 1139:Distinguishable points 547:preliminary definitions 308:Preliminary definitions 1674:fully normal Hausdorff 1291: 1131:Separated by function 259:and related fields of 252: 134:(completely Hausdorff) 1879:(has all of the non-R 1857:axioms, among others) 1703:is strictly between T 1607:for the open sets of 1289: 1215:Disjoint closed sets 249: 1729:cocountable topology 1372:Regular Hausdorff (T 1364:Completely Hausdorff 1179:Completely Hausdorff 904:if, given any point 833:if, given any point 803:completely Hausdorff 510:equals the preimage 1419:Completely normal T 1407:Normal Hausdorff (T 1391:Completely regular 1276:Kolmogorov quotient 1184:Perfectly Hausdorff 920:does not belong to 849:does not belong to 691:functional analysis 463:continuous function 152:(regular Hausdorff) 1819:, 16.6(C), p. 438. 1807:, 16.6(D), p. 438. 1425:Completely normal 1367:(No special name) 1359:(No special name) 1292: 1204:Completely regular 901:completely regular 461:if there exists a 318:topological spaces 265:topological spaces 253: 205:(completely normal 187:(normal Hausdorff) 35:topological spaces 1917:Separation axioms 1717:cofinite topology 1676:, if it is both T 1601:regular open sets 1453: 1452: 1449:Perfectly normal 1319:(No requirement) 1251: 1250: 1239:Completely normal 1026:completely normal 1013:, if it is both T 954:, if it is both T 884:, if it is both T 874:regular Hausdorff 577:topological space 269:separation axioms 244: 243: 225:(perfectly normal 30:Separation axioms 1929: 1878: 1864:General topology 1850: 1820: 1814: 1808: 1802: 1796: 1795:, 16.17, p. 443. 1790: 1784: 1783:, 16.16, p. 442. 1778: 1772: 1766: 1750:General topology 1635:is contained in 1294: 1209:Perfectly normal 1160:Distinct points 1117: 1068:perfectly normal 1003:normal Hausdorff 541:Main definitions 322:separated spaces 316:(and points) in 277:Andrey Tychonoff 227: Hausdorff) 222: 217: 207: Hausdorff) 202: 197: 184: 179: 164: 163: 149: 144: 131: 126: 111: 110: 95: 90: 77: 72: 59: 54: 26: 1937: 1936: 1932: 1931: 1930: 1928: 1927: 1926: 1907: 1906: 1892: 1884: 1875: 1860: 1856: 1847: 1832: 1829: 1824: 1823: 1815: 1811: 1803: 1799: 1791: 1787: 1779: 1775: 1767: 1763: 1758: 1746: 1738: 1726: 1722: 1714: 1710: 1706: 1699:The axiom that 1691: 1687: 1683: 1679: 1669: 1657:star refinement 1586: 1554: 1519: 1510: 1506: 1501: 1494: 1490: 1486: 1482: 1478: 1466: 1462: 1458: 1445: 1433: 1422: 1414:Normal regular 1410: 1399: 1387: 1375: 1356: 1348: 1341: 1333: 1327: 1316: 1307: 1300: 1282: 1273: 1269: 1265: 1261: 1256: 1230:Separated sets 1113: 1109: 1100: 1095: 1088: 1058: 1053: 1046: 1016: 1011: 993: 990:if it is both R 976:Urysohn's lemma 957: 948: 941: 908:and closed set 891: 887: 882: 864: 837:and closed set 820: 811: 793: 779: 766: 762: 758: 741: 723: 720:space is also R 719: 705: 680: 676: 672: 668: 646: 623: 610: 592: 563: 559: 543: 538: 468:from the space 310: 240: 226: 220: 218: 215: 206: 200: 198: 195: 182: 180: 177: 165: 161: 160: 147: 145: 142: 129: 127: 124: 112: 108: 106: 93: 91: 88: 75: 73: 70: 57: 55: 52: 32: 24: 17: 12: 11: 5: 1935: 1933: 1925: 1924: 1919: 1909: 1908: 1905: 1904: 1903:from Schechter 1898: 1891: 1890:External links 1888: 1887: 1886: 1880: 1873: 1858: 1852: 1845: 1828: 1825: 1822: 1821: 1817:Schechter 1997 1809: 1805:Schechter 1997 1797: 1793:Schechter 1997 1785: 1781:Schechter 1997 1773: 1769:Schechter 1997 1760: 1759: 1757: 1754: 1753: 1752: 1745: 1742: 1741: 1740: 1736: 1724: 1720: 1712: 1708: 1704: 1697: 1689: 1685: 1681: 1677: 1667: 1640: 1612: 1588: 1584: 1564:weak Hausdorff 1556: 1552: 1518: 1515: 1508: 1504: 1499: 1492: 1488: 1484: 1480: 1476: 1464: 1460: 1456: 1451: 1450: 1447: 1443: 1439: 1438: 1435: 1431: 1427: 1426: 1423: 1420: 1416: 1415: 1412: 1408: 1404: 1403: 1400: 1397: 1393: 1392: 1389: 1385: 1381: 1380: 1377: 1373: 1369: 1368: 1365: 1361: 1360: 1357: 1354: 1350: 1349: 1346: 1343: 1339: 1335: 1334: 1331: 1328: 1325: 1321: 1320: 1317: 1314: 1310: 1309: 1305: 1302: 1298: 1280: 1271: 1267: 1263: 1259: 1255: 1252: 1249: 1248: 1245:discrete space 1241: 1236: 1231: 1227: 1226: 1221: 1216: 1212: 1211: 1206: 1201: 1196: 1191: 1187: 1186: 1181: 1176: 1171: 1166: 1161: 1157: 1156: 1154: 1152: 1150: 1145: 1140: 1136: 1135: 1132: 1129: 1126: 1123: 1120: 1111: 1107: 1103: 1102: 1098: 1093: 1086: 1072: 1060: 1056: 1051: 1044: 1030: 1018: 1014: 1009: 995: 991: 987:normal regular 979: 959: 955: 946: 939: 925: 893: 889: 885: 880: 866: 862: 822: 818: 809: 795: 791: 777: 768: 764: 760: 756: 739: 725: 721: 717: 703: 694: 678: 674: 670: 666: 644: 635: 634:are separated. 621: 612: 608: 590: 561: 557: 542: 539: 531:Separated sets 376:neighbourhoods 314:separated sets 309: 306: 295:Trennungsaxiom 286:like those of 242: 241: 239: 238: 232: 229: 228: 223: 214: 209: 208: 203: 194: 189: 188: 185: 176: 171: 170: 167: 159: 154: 153: 150: 141: 136: 135: 132: 123: 118: 117: 114: 105: 100: 99: 96: 87: 82: 81: 78: 69: 64: 63: 60: 51: 46: 45: 44:classification 38: 37: 15: 13: 10: 9: 6: 4: 3: 2: 1934: 1923: 1920: 1918: 1915: 1914: 1912: 1902: 1899: 1897: 1894: 1893: 1889: 1883: 1876: 1874:0-486-43479-6 1870: 1866: 1865: 1859: 1855: 1848: 1842: 1838: 1837: 1831: 1830: 1826: 1818: 1813: 1810: 1806: 1801: 1798: 1794: 1789: 1786: 1782: 1777: 1774: 1770: 1765: 1762: 1755: 1751: 1748: 1747: 1743: 1734: 1730: 1718: 1702: 1698: 1695: 1675: 1671: 1670: 1662: 1658: 1654: 1650: 1649: 1644: 1641: 1638: 1634: 1630: 1626: 1622: 1621: 1620:quasi-regular 1616: 1613: 1610: 1606: 1602: 1598: 1597: 1592: 1589: 1582: 1579:is closed in 1578: 1574: 1570: 1566: 1565: 1560: 1557: 1550: 1546: 1542: 1538: 1534: 1533: 1528: 1525: 1524: 1523: 1516: 1514: 1512: 1496: 1473: 1470: 1448: 1441: 1440: 1436: 1429: 1428: 1424: 1418: 1417: 1413: 1406: 1405: 1401: 1395: 1394: 1390: 1383: 1382: 1378: 1371: 1370: 1366: 1363: 1362: 1358: 1352: 1351: 1344: 1337: 1336: 1329: 1323: 1322: 1318: 1312: 1311: 1303: 1296: 1295: 1288: 1284: 1277: 1253: 1247: 1246: 1242: 1240: 1235: 1232: 1229: 1228: 1225: 1220: 1217: 1214: 1213: 1210: 1205: 1202: 1200: 1195: 1192: 1189: 1188: 1185: 1182: 1180: 1177: 1175: 1172: 1170: 1167: 1165: 1162: 1159: 1158: 1155: 1153: 1151: 1149: 1146: 1144: 1141: 1138: 1137: 1133: 1130: 1127: 1124: 1121: 1119: 1118: 1115: 1096: 1089: 1082: 1081: 1076: 1073: 1070: 1069: 1064: 1061: 1054: 1047: 1040: 1039: 1034: 1031: 1028: 1027: 1022: 1019: 1012: 1005: 1004: 999: 996: 989: 988: 983: 980: 977: 973: 969: 968: 963: 960: 953: 949: 942: 935: 934: 929: 926: 923: 919: 915: 911: 907: 903: 902: 897: 894: 883: 876: 875: 870: 867: 860: 856: 852: 848: 844: 840: 836: 832: 831: 826: 823: 816: 812: 805: 804: 799: 796: 789: 785: 781: 780: 772: 769: 754: 750: 746: 742: 735: 734: 729: 726: 715: 711: 707: 706: 698: 695: 692: 688: 687:FrĂ©chet space 684: 664: 660: 656: 652: 648: 647: 639: 636: 633: 629: 625: 624: 616: 613: 606: 602: 598: 594: 593: 585: 582: 581: 580: 578: 574: 569: 565: 555: 550: 548: 540: 536: 532: 527: 523: 521: 517: 513: 509: 505: 501: 497: 493: 489: 485: 482: 478: 475: 471: 467: 464: 460: 456: 452: 448: 444: 439: 437: 433: 429: 425: 420: 416: 412: 408: 404: 400: 396: 392: 387: 385: 381: 377: 373: 369: 365: 361: 357: 352: 350: 346: 342: 338: 334: 330: 329:disjoint sets 325: 323: 319: 315: 307: 305: 303: 298: 296: 293: 289: 285: 280: 278: 274: 270: 266: 262: 258: 248: 237: 234: 233: 230: 224: 219: 210: 204: 199: 190: 186: 181: 172: 168: 166: 155: 151: 146: 137: 133: 128: 119: 115: 113: 101: 97: 92: 83: 79: 74: 65: 61: 56: 47: 43: 39: 36: 31: 27: 22: 1881: 1863: 1853: 1835: 1812: 1800: 1788: 1776: 1764: 1739:(Hausdorff). 1700: 1673: 1664: 1660: 1655:has an open 1648:fully normal 1646: 1642: 1636: 1632: 1628: 1624: 1618: 1614: 1608: 1594: 1590: 1580: 1576: 1572: 1568: 1562: 1558: 1548: 1544: 1540: 1536: 1530: 1526: 1520: 1513: 1497: 1474: 1469:abbreviation 1454: 1384:Tychonoff (T 1338:Hausdorff (T 1257: 1243: 1233: 1218: 1104: 1091: 1084: 1078: 1074: 1066: 1062: 1050:completely T 1049: 1042: 1036: 1032: 1024: 1020: 1007: 1001: 997: 985: 981: 971: 965: 961: 951: 945:completely T 944: 937: 931: 927: 921: 917: 913: 909: 905: 899: 895: 878: 872: 868: 858: 854: 850: 846: 842: 838: 834: 828: 824: 814: 808:completely T 807: 801: 797: 787: 783: 774: 770: 752: 748: 744: 737: 731: 727: 713: 709: 700: 696: 682: 662: 658: 654: 650: 641: 637: 631: 627: 618: 614: 600: 596: 587: 583: 572: 570: 566: 551: 544: 524: 519: 515: 511: 507: 503: 499: 495: 491: 487: 483: 476: 469: 465: 458: 454: 450: 446: 442: 440: 435: 431: 427: 423: 418: 414: 410: 406: 398: 394: 390: 388: 371: 367: 363: 359: 355: 353: 348: 340: 326: 321: 311: 299: 294: 281: 272: 268: 254: 122:completely T 62:(Kolmogorov) 29: 1733:uncountably 1694:paracompact 1596:semiregular 1092:perfectly T 575:is again a 389:Two points 261:mathematics 169:(Tychonoff) 98:(Hausdorff) 1911:Categories 1846:0126227608 1827:References 1684:space is T 1653:open cover 1148:Preregular 1122:Separated 916:such that 845:such that 710:preregular 651:accessible 597:Kolmogorov 514:({0}) and 506:such that 288:set theory 42:Kolmogorov 1771:, p. 441. 1692:space is 1651:if every 1547:} equals 1194:Symmetric 1169:Hausdorff 1143:Symmetric 933:Tychonoff 745:separated 733:Hausdorff 628:symmetric 474:real line 419:separated 399:separated 349:separated 116:(Urysohn) 80:(FrĂ©chet) 1922:Topology 1744:See also 1396:Normal T 1379:Regular 1308:version 481:preimage 441:Subsets 380:open set 333:distinct 275:, after 257:topology 1666:fully T 1603:form a 1599:if the 1402:Normal 1301:version 1199:Regular 1174:Urysohn 1164:FrĂ©chet 830:regular 784:Urysohn 655:FrĂ©chet 549:above. 522:({1}). 518:equals 472:to the 434:} and { 403:closure 384:closure 345:subsets 337:unequal 251:points. 236:History 162:3½ 1871:  1851:(has R 1843:  1234:always 1224:Normal 1219:always 967:normal 292:German 284:axioms 221:  201:  183:  148:  130:  109:½ 94:  76:  58:  1756:Notes 1707:and T 1672:, or 1532:sober 1304:Non-T 1258:The T 1083:, or 1041:, or 1006:, or 950:, or 936:, or 877:, or 806:, or 782:, or 759:and R 736:, or 708:, or 673:and R 649:, or 626:, or 595:, or 498:from 1869:ISBN 1841:ISBN 1605:base 1270:is R 857:and 665:is T 603:are 533:and 526:on. 449:are 445:and 426:and 417:are 409:and 397:are 393:and 370:are 362:and 354:Let 331:and 1731:on 1663:is 1645:is 1617:is 1593:is 1571:to 1561:is 1529:is 1090:or 1077:is 1065:is 1048:or 1035:is 1023:is 1000:is 984:is 964:is 930:is 912:in 898:is 871:is 841:in 827:is 800:is 773:is 743:or 730:is 699:is 689:in 653:or 640:is 617:is 586:is 502:to 413:of 366:in 255:In 33:in 1913:: 1659:. 1386:3½ 1355:2½ 978:.) 943:, 940:3½ 890:2½ 819:2½ 792:2½ 778:2½ 693:.) 579:. 386:. 279:. 1882:i 1877:. 1854:i 1849:. 1737:2 1725:2 1721:1 1713:1 1709:2 1705:1 1690:4 1686:4 1682:4 1678:1 1668:4 1661:X 1643:X 1639:. 1637:G 1633:H 1629:H 1625:G 1615:X 1609:X 1591:X 1587:. 1585:1 1581:X 1577:f 1573:X 1569:f 1559:X 1555:. 1553:0 1549:C 1545:p 1541:p 1537:C 1527:X 1509:1 1505:0 1503:R 1500:0 1493:5 1489:0 1485:0 1481:5 1477:2 1465:0 1461:0 1457:0 1446:) 1444:6 1434:) 1432:5 1421:0 1411:) 1409:4 1398:0 1388:) 1376:) 1374:3 1353:T 1347:1 1345:R 1342:) 1340:2 1332:0 1330:R 1326:1 1324:T 1315:0 1313:T 1306:0 1299:0 1297:T 1281:0 1279:T 1272:1 1268:0 1264:0 1260:0 1112:1 1108:1 1106:T 1099:0 1094:4 1087:6 1085:T 1075:X 1063:X 1057:1 1052:4 1045:5 1043:T 1033:X 1021:X 1015:1 1010:4 1008:T 998:X 992:0 982:X 972:X 962:X 956:0 947:3 938:T 928:X 922:F 918:x 914:X 910:F 906:x 896:X 892:. 886:0 881:3 879:T 869:X 865:. 863:1 859:F 855:x 851:F 847:x 843:X 839:F 835:x 825:X 821:. 815:X 810:2 798:X 788:X 776:T 771:X 767:. 765:1 761:1 757:0 753:X 749:X 740:2 738:T 728:X 724:. 722:0 718:1 714:X 704:1 702:R 697:X 683:X 679:1 675:0 671:0 667:1 663:X 659:X 645:1 643:T 638:X 632:X 622:0 620:R 615:X 609:0 601:X 591:0 589:T 584:X 573:X 562:3 558:4 537:. 520:f 516:B 512:f 508:A 504:R 500:X 496:f 488:f 484:f 477:R 470:X 466:f 447:B 443:A 436:y 432:x 428:y 424:x 415:X 411:B 407:A 395:y 391:x 368:X 364:y 360:x 356:X 216:6 213:T 196:5 193:T 178:4 175:T 158:T 143:3 140:T 125:2 107:2 104:T 89:2 86:T 71:1 68:T 53:0 50:T 23:.

Index

Axiom schema of separation
Separation axioms
topological spaces
Kolmogorov
T0
T1
T2
T2½
completely T2
T3
T
T4
T5
T6
History
Illustrations of the properties of Hausdorffness, regularity and normality
topology
mathematics
topological spaces
Andrey Tychonoff
axioms
set theory
German
separation axioms have varied over time
separated sets
topological spaces
disjoint sets
distinct
unequal
subsets

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