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Lebesgue covering dimension

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The top half of the second image shows a cover (colored) of a planar shape (dark), where all of the shape's points are contained in anywhere from one to all four of the cover's sets. The bottom illustrates that any attempt to refine said cover such that no point would be contained in more than
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The first image shows a refinement (on the bottom) of a colored cover (on the top) of a black circular line. Note how in the refinement, no point on the circle is contained in more than two sets, and also how the sets link to one another to form a "chain".
128:, the Lebesgue covering dimension is just the ordinary Euclidean dimension: zero for points, one for lines, two for planes, and so on. However, not all topological spaces have this kind of "obvious" 743:
The empty set has covering dimension -1: for any open cover of the empty set, each point of the empty set is not contained in any element of the cover, so the order of any open cover is 0.
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can be refined so that any point of the disk is contained in no more than three open sets, while two are in general not sufficient. The covering dimension of the disk is thus two.
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two open arcs. That is, whatever collection of arcs we begin with, some can be discarded or shrunk, such that the remainder still covers the circle but with simple overlaps.
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sets—ultimately fails at the intersection of set borders. Thus, a planar shape is not "webby": it cannot be covered with "chains", per se. Instead, it proves to be
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arcs. The circle has dimension one, by this definition, because any such cover can be further refined to the stage where a given point
175: + 1 covering sets. This is the gist of the formal definition below. The goal of the definition is to provide a number (an 132:, and so a precise definition is needed in such cases. The definition proceeds by examining what happens when the space is covered by 1658:, American Mathematical Society, Collected works series, vol. 4, American Mathematical Society, p. xxiii, footnote 3, 179:) that describes the space, and does not change as the space is continuously deformed; that is, a number that is invariant under 1518: 1798: 17: 1855:. Publications de l'Institut de Mathématique de l'Université de Strasbourg (in French). Vol. III. Paris: Hermann. 2195: 2145: 2039: 2005: 1967: 1901: 1830: 1749: 1698: 1663: 186:
The general idea is illustrated in the diagrams below, which show a cover and refinements of a circle and a square.
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with respect to the covering dimension if every open cover of the space has a refinement consisting of
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open sets, meaning any point in the space is contained in exactly one open set of this refinement.
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Lebesgue's discovery led later to the introduction by E. Čech of the covering dimension
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in some sense. More rigorously put, its topological dimension must be greater than 1.
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spaces have the same covering dimension. That is, the covering dimension is a
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Encyclopaedia of Mathematical Sciences, Volume 17, General Topology I
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Ostrand, Phillip A. (1971). "Covering dimension in general spaces".
376:(if it exists) for which each point of the space belongs to at most 2252: 2215: 2140: 999: 271: 133: 1262: + 1. In particular, this holds for all metric spaces. 2262: 176: 724:
exists, the space is said to have infinite covering dimension.
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The first formal definition of covering dimension was given by
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sets in the cover. This idea leads to the definitions of the
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Topologically invariant definition of the dimension of a space
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used closed "bricks" to study covering dimension in 1921.
1789:. Undergraduate Texts in Mathematics (Second ed.). 1439: 1419: 1399: 1379: 1331: 1303: 1238: 1208: 1128: 1080: 1021: 977: 938: 918: 879: 845: 789: 750:
will have a refinement consisting of a collection of
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As a special case, a non-empty topological space is
1630: 1268:The Lebesgue covering dimension coincides with the 1785:Edgar, Gerald A. (2008). "Topological Dimension". 1715: 1445: 1425: 1405: 1385: 1365: 1309: 1248: 1218: 1138: 1090: 1031: 990: 963: 924: 904: 854: 804: 691: 636: 606: 578: 505: 470: 423: 351: 303: 108:is one of several different ways of defining the 2376: 1962:, Gerald A.Edgar, editor, Addison-Wesley (1993) 155:. The covering dimension is the smallest number 1867: 1872:. Princeton Mathematical Series. Vol. 4. 1492:of a space: a space with asymptotic dimension 2086: 1853:Topologie algébrique et théorie des faisceaux 912:is continuous, then there is an extension of 644:can always be chosen to be finite. Thus, if 1185:Relationships to other notions of dimension 2093: 2079: 284:such that their union is the whole space, 1979:, (1928) B.G Teubner Publishers, Leipzig. 1868:Hurewicz, Witold; Wallman, Henry (1941). 1815: 1734: 1683: 1648: 1613: 1598:"The origins of the concept of dimension" 835:The covering dimension of a normal space 792: 80:Learn how and when to remove this message 1847: 1636: 1556: 237: 208: 192: 43:This article includes a list of general 1918: 1888: 1787:Measure, topology, and fractal geometry 1721: 1550: 1009:Ostrand's theorem on colored dimension. 382:open sets in the cover: in other words 14: 2377: 1433:larger than the covering dimension of 556:is defined to be the minimum value of 260:A modern definition is as follows. An 159:such that for every cover, there is a 119: 2074: 1989: 1784: 1232:(of any size) has an open refinement 2024:The Fundamentals of Dimension Theory 1595: 964:{\displaystyle g:X\rightarrow S^{n}} 905:{\displaystyle f:A\rightarrow S^{n}} 233: 29: 1956:General Spaces and Cartesian Spaces 1589: 1283:is less than or equal to the large 1241: 1211: 1131: 1083: 1024: 629: 599: 571: 498: 463: 344: 213:Refinement of the cover of a square 197:Refinement of the cover of a circle 24: 2030:, (1993) A. V. Arkhangel'skii and 1993:Dimension Theory of General Spaces 1940: 1655:Collected Works of Witold Hurewicz 1015:is a normal topological space and 686: 562:such that every finite open cover 418: 49:it lacks sufficient corresponding 25: 2396: 2046: 765:Similarly, any open cover of the 620: + 1. The refinement 2159: 2034:(Eds.), Springer-Verlag, Berlin 1519:Carathéodory's extension theorem 805:{\displaystyle \mathbb {E} ^{n}} 253:, based on an earlier result of 139:In general, a topological space 34: 1896:(2nd ed.). Prentice-Hall. 1249:{\displaystyle {\mathfrak {B}}} 1219:{\displaystyle {\mathfrak {A}}} 1139:{\displaystyle {\mathfrak {A}}} 1091:{\displaystyle {\mathfrak {B}}} 1050:} is a locally finite cover of 1032:{\displaystyle {\mathfrak {A}}} 637:{\displaystyle {\mathfrak {B}}} 607:{\displaystyle {\mathfrak {B}}} 579:{\displaystyle {\mathfrak {A}}} 506:{\displaystyle {\mathfrak {B}}} 471:{\displaystyle {\mathfrak {A}}} 352:{\displaystyle {\mathfrak {A}}} 304:{\displaystyle \cup _{\alpha }} 1772:Godement 1973, II.5.12, p. 236 1766: 1727: 1676: 1642: 1508:-dimensional "at every scale". 1477:-ball intersects with at most 1354: 1342: 948: 889: 758:of the circle is contained in 13: 1: 2100: 1945: 1778: 1202:, such that every open cover 819: 718:distinct. If no such minimal 1366:{\displaystyle H^{i}(X,A)=0} 1290:The covering dimension of a 1279:The covering dimension of a 746:Any given open cover of the 7: 2059:Encyclopedia of Mathematics 1816:Engelking, Ryszard (1978). 1735:Engelking, Ryszard (1978). 1684:Engelking, Ryszard (1978). 1524:Geometric set cover problem 1512: 1317:is greater or equal to its 738: 98:Lebesgue covering dimension 10: 2401: 1998:Cambridge University Press 1874:Princeton University Press 1266:Lebesgue covering theorem. 692:{\displaystyle \emptyset } 424:{\displaystyle \emptyset } 2361: 2340: 2276: 2214: 2168: 2157: 2108: 1983: 1921:General Topology and Appl 370:} is the smallest number 1544: 1490:Assouad–Nagata dimension 1190:For a paracompact space 1174:, and together covering 1062:+ 1, then, for each 1 ≤ 489:} is another open cover 163:in which every point in 1990:Pears, Alan R. (1975). 1602:Colloquium Mathematicum 1570:Fundamenta Mathematicae 1539:Point-finite collection 1319:cohomological dimension 862:if and only if for any 812:has covering dimension 769:in the two-dimensional 590:has an open refinement 550:of a topological space 264:of a topological space 114:topologically invariant 64:more precise citations. 1615:10.4064/cm-42-1-95-110 1583:10.4064/fm-2-1-256-285 1447: 1427: 1407: 1387: 1367: 1311: 1250: 1220: 1140: 1092: 1033: 992: 965: 926: 906: 856: 855:{\displaystyle \leq n} 806: 693: 638: 608: 580: 507: 472: 425: 353: 305: 246: 214: 198: 1733:Proposition 3.2.2 of 1682:Proposition 1.6.9 of 1448: 1428: 1408: 1393:of abelian groups on 1388: 1368: 1312: 1251: 1221: 1141: 1093: 1034: 993: 991:{\displaystyle S^{n}} 966: 927: 907: 857: 830:topological invariant 807: 694: 639: 609: 581: 535:is contained in some 508: 473: 426: 354: 306: 241: 212: 196: 151:lies inside of their 102:topological dimension 18:Topological dimension 2277:Dimensions by number 2054:"Lebesgue dimension" 1960:Classics on Fractals 1486:asymptotic dimension 1437: 1417: 1397: 1377: 1329: 1325:), that is, one has 1301: 1236: 1206: 1126: 1078: 1019: 975: 936: 916: 877: 843: 787: 776:More generally, the 683: 624: 594: 566: 493: 458: 415: 339: 288: 145:covered by open sets 1793:. pp. 85–114. 1650:Kuperberg, Krystyna 1285:inductive dimension 1003:-dimensional sphere 120:Informal discussion 2206:Degrees of freedom 2109:Dimensional spaces 1443: 1423: 1403: 1383: 1363: 1307: 1274:simplicial complex 1246: 1216: 1136: 1088: 1029: 988: 961: 922: 902: 852: 802: 689: 634: 604: 576: 548:covering dimension 524:}, such that each 503: 468: 421: 349: 301: 247: 215: 199: 112:of the space in a 2372: 2371: 2181:Lebesgue covering 2146:Algebraic variety 2022:V. V. Fedorchuk, 1977:Dimensionstheorie 1890:Munkres, James R. 1800:978-0-387-74748-4 1596:Duda, R. (1979). 1534:Metacompact space 1446:{\displaystyle X} 1426:{\displaystyle i} 1406:{\displaystyle X} 1386:{\displaystyle A} 1321:(in the sense of 1310:{\displaystyle X} 925:{\displaystyle f} 454:of an open cover 335:of an open cover 234:Formal definition 231: 230: 106:topological space 90: 89: 82: 16:(Redirected from 2392: 2385:Dimension theory 2169:Other dimensions 2163: 2131:Projective space 2095: 2088: 2081: 2072: 2071: 2067: 2032:L. S. Pontryagin 2019: 1936: 1915: 1885: 1870:Dimension Theory 1864: 1844: 1824: 1819:Dimension theory 1812: 1773: 1770: 1764: 1763: 1743: 1738:Dimension theory 1731: 1725: 1719: 1713: 1712: 1692: 1687:Dimension theory 1680: 1674: 1672: 1646: 1640: 1634: 1628: 1627: 1617: 1593: 1587: 1586: 1566: 1554: 1529:Dimension theory 1507: 1503: 1499: 1495: 1483: 1476: 1472: 1464: 1452: 1450: 1449: 1444: 1432: 1430: 1429: 1424: 1412: 1410: 1409: 1404: 1392: 1390: 1389: 1384: 1373:for every sheaf 1372: 1370: 1369: 1364: 1341: 1340: 1316: 1314: 1313: 1308: 1270:affine dimension 1261: 1255: 1253: 1252: 1247: 1245: 1244: 1231: 1225: 1223: 1222: 1217: 1215: 1214: 1201: 1195: 1179: 1172: 1168: 1161: 1157: 1151: 1145: 1143: 1142: 1137: 1135: 1134: 1120: 1116: 1110: 1103: 1097: 1095: 1094: 1089: 1087: 1086: 1073: 1067: 1061: 1055: 1048: 1044: 1038: 1036: 1035: 1030: 1028: 1027: 1014: 997: 995: 994: 989: 987: 986: 970: 968: 967: 962: 960: 959: 931: 929: 928: 923: 911: 909: 908: 903: 901: 900: 861: 859: 858: 853: 811: 809: 808: 803: 801: 800: 795: 729:zero-dimensional 723: 715: 709: 702: 698: 696: 695: 690: 675: 669: 665: 657: 653: 649: 643: 641: 640: 635: 633: 632: 619: 613: 611: 610: 605: 603: 602: 585: 583: 582: 577: 575: 574: 561: 555: 544: 540: 533: 529: 522: 518: 512: 510: 509: 504: 502: 501: 487: 483: 477: 475: 474: 469: 467: 466: 447: 441: 434: 430: 428: 427: 422: 407: 401: 397: 389: 385: 381: 375: 368: 364: 358: 356: 355: 350: 348: 347: 326: 319: 315: 310: 308: 307: 302: 300: 299: 282: 278: 269: 189: 188: 171:of no more than 126:Euclidean spaces 85: 78: 74: 71: 65: 60:this article by 51:inline citations 38: 37: 30: 21: 2400: 2399: 2395: 2394: 2393: 2391: 2390: 2389: 2375: 2374: 2373: 2368: 2357: 2336: 2272: 2210: 2164: 2155: 2121:Euclidean space 2104: 2099: 2052: 2049: 2026:, appearing in 2008: 1986: 1948: 1943: 1941:Further reading 1904: 1849:Godement, Roger 1833: 1822: 1801: 1791:Springer-Verlag 1781: 1776: 1771: 1767: 1752: 1741: 1732: 1728: 1720: 1716: 1701: 1690: 1681: 1677: 1666: 1647: 1643: 1635: 1631: 1594: 1590: 1564: 1558:Lebesgue, Henri 1555: 1551: 1547: 1515: 1505: 1501: 1497: 1493: 1478: 1474: 1467: 1462: 1438: 1435: 1434: 1418: 1415: 1414: 1398: 1395: 1394: 1378: 1375: 1374: 1336: 1332: 1330: 1327: 1326: 1302: 1299: 1298: 1257: 1240: 1239: 1237: 1234: 1233: 1227: 1210: 1209: 1207: 1204: 1203: 1197: 1191: 1187: 1175: 1173: 1170: 1164: 1162: 1159: 1153: 1147: 1130: 1129: 1127: 1124: 1123: 1121: 1118: 1112: 1106: 1104: 1099: 1082: 1081: 1079: 1076: 1075: 1069: 1063: 1057: 1051: 1049: 1046: 1040: 1023: 1022: 1020: 1017: 1016: 1012: 982: 978: 976: 973: 972: 955: 951: 937: 934: 933: 917: 914: 913: 896: 892: 878: 875: 874: 844: 841: 840: 822: 796: 791: 790: 788: 785: 784: 782:Euclidean space 741: 719: 717: 711: 707: 705: 700: 684: 681: 680: 678: 677: 671: 667: 663: 661: 660: 655: 651: 645: 628: 627: 625: 622: 621: 615: 598: 597: 595: 592: 591: 570: 569: 567: 564: 563: 557: 551: 545: 542: 536: 534: 531: 525: 523: 520: 514: 497: 496: 494: 491: 490: 488: 485: 479: 462: 461: 459: 456: 455: 449: 443: 439: 437: 432: 416: 413: 412: 410: 409: 403: 399: 395: 393: 392: 387: 383: 377: 371: 369: 366: 360: 343: 342: 340: 337: 336: 322: 320: 317: 311: 295: 291: 289: 286: 285: 283: 280: 274: 270:is a family of 265: 236: 122: 86: 75: 69: 66: 56:Please help to 55: 39: 35: 28: 23: 22: 15: 12: 11: 5: 2398: 2388: 2387: 2370: 2369: 2362: 2359: 2358: 2356: 2355: 2350: 2344: 2342: 2338: 2337: 2335: 2334: 2326: 2321: 2316: 2311: 2306: 2301: 2296: 2291: 2286: 2280: 2278: 2274: 2273: 2271: 2270: 2265: 2260: 2258:Cross-polytope 2255: 2250: 2245: 2243:Hyperrectangle 2240: 2235: 2230: 2224: 2222: 2212: 2211: 2209: 2208: 2203: 2198: 2193: 2188: 2183: 2178: 2172: 2170: 2166: 2165: 2158: 2156: 2154: 2153: 2148: 2143: 2138: 2133: 2128: 2123: 2118: 2112: 2110: 2106: 2105: 2098: 2097: 2090: 2083: 2075: 2069: 2068: 2048: 2047:External links 2045: 2044: 2043: 2020: 2006: 1985: 1982: 1981: 1980: 1970: 1947: 1944: 1942: 1939: 1938: 1937: 1927:(3): 209–221. 1916: 1902: 1886: 1865: 1845: 1831: 1813: 1799: 1780: 1777: 1775: 1774: 1765: 1750: 1726: 1714: 1699: 1675: 1664: 1652:, ed. 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A 444: 404: 378: 372: 361: 332: 328: 323: 312: 275: 266: 259: 248: 224: 220: 185: 172: 169:intersection 167:lies in the 164: 156: 148: 140: 138: 123: 101: 97: 91: 76: 67: 48: 2353:Codimension 2332:-dimensions 2253:Hypersphere 2136:Free module 1973:Karl Menger 1952:Karl Menger 1577:: 256–285. 1292:paracompact 1256:with order 1056:of order ≤ 748:unit circle 650:is finite, 614:with order 251:Eduard Čech 94:mathematics 62:introducing 2348:Hyperspace 2228:Hyperplane 1946:Historical 1779:References 1608:: 95–110. 1413:and every 820:Properties 452:refinement 262:open cover 161:refinement 70:April 2018 45:references 2238:Hypercube 2216:Polytopes 2196:Minkowski 2191:Hausdorff 2186:Inductive 2151:Spacetime 2102:Dimension 2064:EMS Press 1473:if every 1295:Hausdorff 971:. Here, 949:→ 890:→ 847:≤ 767:unit disk 687:∅ 419:∅ 297:α 293:∪ 272:open sets 134:open sets 130:dimension 110:dimension 2379:Category 2365:Category 2341:See also 2141:Manifold 1894:Topology 1892:(2000). 1851:(1958). 1560:(1921). 1513:See also 739:Examples 733:disjoint 662:∩ ⋅⋅⋅ ∩ 394:∩ ⋅⋅⋅ ∩ 2263:Simplex 2201:Fractal 2066:, 2001 2016:0394604 1933:0288741 1912:3728284 1882:0006493 1861:0102797 1841:0482697 1809:2356043 1760:0482697 1709:0482697 1624:0567548 1323:sheaves 1146:, i.e. 998:is the 760:at most 706:, ..., 438:, ..., 225:thicker 177:integer 143:can be 58:improve 2220:shapes 2038:  2014:  2004:  1984:Modern 1966:  1931:  1910:  1900:  1880:  1859:  1839:  1829:  1807:  1797:  1758:  1748:  1707:  1697:  1662:  1622:  1297:space 546:. The 327:. The 96:, the 47:, but 2324:Eight 2319:Seven 2299:Three 2176:Krull 1823:(PDF) 1742:(PDF) 1691:(PDF) 1565:(PDF) 1545:Notes 1456:In a 873:, if 771:plane 329:order 153:union 116:way. 104:of a 2309:Five 2304:Four 2284:Zero 2218:and 2036:ISBN 2002:ISBN 1964:ISBN 1898:ISBN 1827:ISBN 1795:ISBN 1746:ISBN 1695:ISBN 1660:ISBN 1488:and 752:open 699:for 431:for 2314:Six 2294:Two 2289:One 1610:doi 1579:doi 1504:is 1496:is 1482:+ 1 1471:+ 1 1226:of 1105:= { 1039:= { 1011:If 932:to 869:of 839:is 586:of 513:= { 478:= { 359:= { 333:ply 331:or 221:two 183:. 100:or 92:In 2381:: 2062:, 2056:, 2012:MR 2010:. 2000:. 1996:. 1975:, 1954:, 1929:MR 1923:. 1908:MR 1906:. 1878:MR 1876:. 1857:MR 1837:MR 1835:. 1805:MR 1803:. 1756:MR 1754:. 1705:MR 1703:. 1668:, 1620:MR 1618:. 1606:42 1604:. 1600:. 1567:. 1163:⊆ 1068:≤ 816:. 716:+2 679:= 676:+2 448:+1 411:= 408:+1 321:= 257:. 136:. 2330:n 2094:e 2087:t 2080:v 2042:. 2018:. 1935:. 1925:1 1914:. 1884:. 1863:. 1843:. 1811:. 1762:. 1724:. 1711:. 1673:. 1639:. 1626:. 1612:: 1585:. 1581:: 1575:2 1506:n 1502:n 1498:n 1494:n 1480:n 1475:r 1469:n 1463:r 1453:. 1441:X 1421:i 1401:X 1381:A 1361:0 1358:= 1355:) 1352:A 1349:, 1346:X 1343:( 1338:i 1334:H 1305:X 1287:. 1276:. 1259:n 1242:B 1229:X 1212:A 1199:n 1193:X 1180:. 1177:X 1171:α 1166:U 1160:α 1158:, 1155:i 1149:V 1132:A 1119:α 1117:, 1114:i 1108:V 1101:i 1084:B 1071:n 1065:i 1059:n 1053:X 1047:α 1042:U 1025:A 1013:X 1005:. 1001:n 984:n 980:S 957:n 953:S 946:X 943:: 940:g 920:f 898:n 894:S 887:A 884:: 881:f 871:X 867:A 850:n 837:X 832:. 814:n 798:n 793:E 778:n 756:x 721:n 713:n 708:β 704:1 701:β 673:n 668:β 664:V 659:1 656:β 652:V 647:n 630:B 617:n 600:B 588:X 572:A 559:n 553:X 543:α 538:U 532:β 527:V 521:β 516:V 499:B 486:α 481:U 464:A 445:m 440:α 436:1 433:α 405:m 400:α 396:U 391:1 388:α 384:U 379:m 373:m 367:α 362:U 345:A 324:X 318:α 313:U 281:α 276:U 267:X 173:n 165:X 157:n 149:X 141:X 83:) 77:( 72:) 68:( 54:. 20:)

Index

Topological dimension
references
inline citations
improve
introducing
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mathematics
topological space
dimension
topologically invariant
Euclidean spaces
dimension
open sets
covered by open sets
union
refinement
intersection
integer
homeomorphisms



Henri Lebesgue
Eduard Čech
Henri Lebesgue
open cover
open sets
refinement
zero-dimensional
disjoint

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