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Algebraic closure

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There are many countable algebraically closed fields within the complex numbers, and strictly containing the field of algebraic numbers; these are the algebraic closures of
927: 1346: 1419: 1373: 283: 380: 566: 1101:. Since a separable extension of a separable extension is again separable, there are no finite separable extensions of 1454: 438: 1150: 773:{\displaystyle f_{\lambda }-\prod _{i=1}^{d}(x-u_{\lambda ,i})=\sum _{j=0}^{d-1}r_{\lambda ,j}\cdot x^{j}\in R} 208: 1365: 936: 540: 786: 1237: 347: 47: 1498: 1133: 82: 837: 507: 234: 905: 337: 1358:
Brawley, Joel V.; Schnibben, George E. (1989), "2.2 The Algebraic Closure of a Finite Field",
1359: 1213: 51: 1410:. Ergebnisse der Mathematik und ihrer Grenzgebiete. 3. Folge. Vol. 11 (3rd ed.). 1481: 1464: 1429: 1383: 1334: 1012:, because any polynomial with coefficients in this new field has its coefficients in some 8: 1242: 1075: 161: 39: 32: 1008:
can be constructed, etc. The union of all these extensions is the algebraic closure of
257: 191: 1450: 1415: 1369: 1247: 62: 1477: 1460: 1442: 1425: 1379: 1330: 1322: 334: 227: 24: 1449:. Chicago lectures in mathematics (Second ed.). University of Chicago Press. 1411: 1284: 1047: 827: 223: 179: 58: 1280: 1252: 216: 1492: 1326: 1125: 249: 245: 66: 275: 212: 78: 20: 1476:(Corrected reprint of the 2nd ed.). New York: Dover Publications. 1313:
Banaschewski, Bernhard (1992), "Algebraic closure without choice.",
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The separable closure is the full algebraic closure if and only if
265: 1114: 74: 144:
is also the smallest algebraically closed field containing
89:. Because of this essential uniqueness, we often speak of 1038:
It can be shown along the same lines that for any subset
875:, Zorn's lemma implies that there exists a maximal ideal 112:
can be thought of as the largest algebraic extension of
326:{\displaystyle S=\{f_{\lambda }|\lambda \in \Lambda \}} 237:
of the rational numbers, e.g. the algebraic closure of
276:
Existence of an algebraic closure and splitting fields
1153: 939: 908: 840: 789: 633: 569: 543: 510: 441: 428:{\displaystyle u_{\lambda ,1},\ldots ,u_{\lambda ,d}} 383: 350: 286: 1291:. Addison-Wesley publishing Company. pp. 11–12. 1085:containing all (algebraic) separable extensions of 1201: 979: 921: 859: 814: 772: 617:{\displaystyle i\leq {\rm {degree}}(f_{\lambda })} 616: 555: 529: 488: 427: 369: 325: 211:states that the algebraic closure of the field of 260:field that contains a copy of the field of order 1490: 1357: 1361:Infinite Algebraic Extensions of Finite Fields 1209:is a non-separable algebraic field extension. 489:{\displaystyle d={\rm {degree}}(f_{\lambda })} 1105:, of degree > 1. Saying this another way, 152:is any algebraically closed field containing 136:is contained within the algebraic closure of 1312: 1202:{\displaystyle K(X)({\sqrt{X}})\supset K(X)} 320: 293: 69:, and that the algebraic closure of a field 1405: 271:(and is in fact the union of these copies). 1364:, Contemporary Mathematics, vol. 95, 1113:algebraic extension field. It is unique ( 1441: 1406:Fried, Michael D.; Jarden, Moshe (2008). 1299: 1297: 1471: 902:has the property that every polynomial 1491: 1294: 222:The algebraic closure of the field of 980:{\displaystyle x-(u_{\lambda ,i}+M),} 1390: 1265: 1061: 556:{\displaystyle \lambda \in \Lambda } 67:every field has an algebraic closure 1399: 1289:Introduction to commutative algebra 815:{\displaystyle r_{\lambda ,j}\in R} 13: 1035:, and hence in the union itself. 593: 590: 587: 584: 581: 578: 550: 465: 462: 459: 456: 453: 450: 317: 14: 1510: 1093:. This subextension is called a 370:{\displaystyle f_{\lambda }\in S} 174:The algebraic closure of a field 108:The algebraic closure of a field 994:. In the same way, an extension 128:is also an algebraic closure of 124:, then the algebraic closure of 1315:Z. Math. Logik Grundlagen Math. 1474:Algebraic extensions of fields 1351: 1340: 1306: 1274: 1196: 1190: 1181: 1166: 1163: 1157: 971: 946: 860:{\displaystyle r_{\lambda ,j}} 767: 761: 693: 668: 611: 598: 530:{\displaystyle u_{\lambda ,i}} 483: 470: 307: 209:fundamental theorem of algebra 120:is any algebraic extension of 1: 1366:American Mathematical Society 1258: 256:, the algebraic closure is a 167:form an algebraic closure of 1025:, and then its roots are in 922:{\displaystyle f_{\lambda }} 500:be the polynomial ring over 116:. To see this, note that if 7: 1231: 987:and hence has all roots in 201: 140:. The algebraic closure of 10: 1515: 1472:McCarthy, Paul J. (1991). 1238:Algebraically closed field 871:is strictly smaller than 377:, introduce new variables 1303:Kaplansky (1972) pp.74-76 933:splits as the product of 235:transcendental extensions 16:Algebraic field extension 1327:10.1002/malq.19920380136 1021:with sufficiently large 65:, it can be shown that 1347:Mathoverflow discussion 1220:is the Galois group of 1143:is transcendental over 338:irreducible polynomials 156:, then the elements of 1203: 981: 923: 861: 816: 774: 725: 667: 618: 557: 531: 490: 429: 371: 327: 1214:absolute Galois group 1204: 1066:An algebraic closure 982: 929:with coefficients in 924: 862: 817: 775: 699: 647: 619: 558: 532: 491: 430: 372: 328: 101:algebraic closure of 93:algebraic closure of 50:. It is one of many 1396:McCarthy (1991) p.22 1271:McCarthy (1991) p.21 1151: 937: 906: 838: 787: 631: 567: 541: 508: 439: 381: 348: 284: 190:is infinite, and is 48:algebraically closed 1243:Algebraic extension 1076:separable extension 40:algebraic extension 1368:, pp. 22–23, 1199: 1128:. For example, if 1109:is contained in a 1074:contains a unique 977: 919: 857: 812: 770: 614: 553: 527: 486: 425: 367: 333:be the set of all 323: 264:for each positive 258:countably infinite 192:countably infinite 1443:Kaplansky, Irving 1421:978-3-540-77269-9 1375:978-0-8218-5428-0 1248:Puiseux expansion 1179: 1095:separable closure 1062:Separable closure 1046:, there exists a 834:generated by the 228:algebraic numbers 63:ultrafilter lemma 29:algebraic closure 1506: 1499:Field extensions 1485: 1468: 1447:Fields and rings 1434: 1433: 1408:Field arithmetic 1403: 1397: 1394: 1388: 1386: 1355: 1349: 1344: 1338: 1337: 1310: 1304: 1301: 1292: 1278: 1272: 1269: 1212:In general, the 1208: 1206: 1205: 1200: 1180: 1178: 1170: 1111:separably-closed 986: 984: 983: 978: 964: 963: 928: 926: 925: 920: 918: 917: 866: 864: 863: 858: 856: 855: 821: 819: 818: 813: 805: 804: 779: 777: 776: 771: 754: 753: 741: 740: 724: 713: 692: 691: 666: 661: 643: 642: 623: 621: 620: 615: 610: 609: 597: 596: 562: 560: 559: 554: 536: 534: 533: 528: 526: 525: 495: 493: 492: 487: 482: 481: 469: 468: 434: 432: 431: 426: 424: 423: 399: 398: 376: 374: 373: 368: 360: 359: 332: 330: 329: 324: 310: 305: 304: 226:is the field of 224:rational numbers 215:is the field of 85:every member of 54:in mathematics. 25:abstract algebra 1514: 1513: 1509: 1508: 1507: 1505: 1504: 1503: 1489: 1488: 1457: 1438: 1437: 1422: 1412:Springer-Verlag 1404: 1400: 1395: 1391: 1376: 1356: 1352: 1345: 1341: 1311: 1307: 1302: 1295: 1285:I. G. Macdonald 1279: 1275: 1270: 1266: 1261: 1234: 1174: 1169: 1152: 1149: 1148: 1064: 1048:splitting field 1034: 1020: 1007: 1000: 993: 953: 949: 938: 935: 934: 913: 909: 907: 904: 903: 893: 845: 841: 839: 836: 835: 794: 790: 788: 785: 784: 749: 745: 730: 726: 714: 703: 681: 677: 662: 651: 638: 634: 632: 629: 628: 605: 601: 577: 576: 568: 565: 564: 542: 539: 538: 515: 511: 509: 506: 505: 477: 473: 449: 448: 440: 437: 436: 413: 409: 388: 384: 382: 379: 378: 355: 351: 349: 346: 345: 306: 300: 296: 285: 282: 281: 278: 217:complex numbers 204: 23:, particularly 17: 12: 11: 5: 1512: 1502: 1501: 1487: 1486: 1469: 1455: 1436: 1435: 1420: 1414:. p. 12. 1398: 1389: 1374: 1350: 1339: 1321:(4): 383–385, 1305: 1293: 1273: 1263: 1262: 1260: 1257: 1256: 1255: 1253:Complete field 1250: 1245: 1240: 1233: 1230: 1198: 1195: 1192: 1189: 1186: 1183: 1177: 1173: 1168: 1165: 1162: 1159: 1156: 1134:characteristic 1132:is a field of 1117:isomorphism). 1063: 1060: 1029: 1016: 1005: 998: 991: 976: 973: 970: 967: 962: 959: 956: 952: 948: 945: 942: 916: 912: 891: 883:that contains 854: 851: 848: 844: 811: 808: 803: 800: 797: 793: 781: 780: 769: 766: 763: 760: 757: 752: 748: 744: 739: 736: 733: 729: 723: 720: 717: 712: 709: 706: 702: 698: 695: 690: 687: 684: 680: 676: 673: 670: 665: 660: 657: 654: 650: 646: 641: 637: 613: 608: 604: 600: 595: 592: 589: 586: 583: 580: 575: 572: 552: 549: 546: 524: 521: 518: 514: 485: 480: 476: 472: 467: 464: 461: 458: 455: 452: 447: 444: 422: 419: 416: 412: 408: 405: 402: 397: 394: 391: 387: 366: 363: 358: 354: 322: 319: 316: 313: 309: 303: 299: 295: 292: 289: 277: 274: 273: 272: 242: 231: 220: 203: 200: 162:algebraic over 97:, rather than 61:or the weaker 15: 9: 6: 4: 3: 2: 1511: 1500: 1497: 1496: 1494: 1483: 1479: 1475: 1470: 1466: 1462: 1458: 1456:0-226-42451-0 1452: 1448: 1444: 1440: 1439: 1431: 1427: 1423: 1417: 1413: 1409: 1402: 1393: 1385: 1381: 1377: 1371: 1367: 1363: 1362: 1354: 1348: 1343: 1336: 1332: 1328: 1324: 1320: 1316: 1309: 1300: 1298: 1290: 1286: 1282: 1277: 1268: 1264: 1254: 1251: 1249: 1246: 1244: 1241: 1239: 1236: 1235: 1229: 1227: 1223: 1219: 1215: 1210: 1193: 1187: 1184: 1175: 1171: 1160: 1154: 1146: 1142: 1138: 1135: 1131: 1127: 1126:perfect field 1123: 1118: 1116: 1112: 1108: 1104: 1100: 1096: 1092: 1088: 1084: 1080: 1077: 1073: 1069: 1059: 1057: 1053: 1049: 1045: 1041: 1036: 1032: 1028: 1024: 1019: 1015: 1011: 1004: 997: 990: 974: 968: 965: 960: 957: 954: 950: 943: 940: 932: 914: 910: 901: 897: 890: 886: 882: 878: 874: 870: 852: 849: 846: 842: 833: 829: 825: 809: 806: 801: 798: 795: 791: 764: 758: 755: 750: 746: 742: 737: 734: 731: 727: 721: 718: 715: 710: 707: 704: 700: 696: 688: 685: 682: 678: 674: 671: 663: 658: 655: 652: 648: 644: 639: 635: 627: 626: 625: 606: 602: 573: 570: 547: 544: 522: 519: 516: 512: 504:generated by 503: 499: 478: 474: 445: 442: 420: 417: 414: 410: 406: 403: 400: 395: 392: 389: 385: 364: 361: 356: 352: 343: 339: 336: 314: 311: 301: 297: 290: 287: 270: 267: 263: 259: 255: 251: 247: 243: 240: 236: 232: 229: 225: 221: 218: 214: 210: 206: 205: 199: 197: 193: 189: 185: 181: 178:has the same 177: 172: 170: 166: 163: 159: 155: 151: 148:, because if 147: 143: 139: 135: 131: 127: 123: 119: 115: 111: 106: 104: 100: 96: 92: 88: 84: 80: 76: 72: 68: 64: 60: 55: 53: 49: 45: 41: 37: 34: 30: 26: 22: 1473: 1446: 1407: 1401: 1392: 1360: 1353: 1342: 1318: 1314: 1308: 1288: 1281:M. F. Atiyah 1276: 1267: 1225: 1221: 1217: 1211: 1144: 1140: 1136: 1129: 1121: 1119: 1110: 1106: 1102: 1098: 1094: 1090: 1086: 1082: 1078: 1071: 1067: 1065: 1055: 1051: 1043: 1039: 1037: 1030: 1026: 1022: 1017: 1013: 1009: 1002: 995: 988: 930: 899: 895: 888: 887:. The field 884: 880: 876: 872: 868: 831: 823: 782: 501: 497: 341: 279: 268: 261: 253: 252:power order 246:finite field 238: 213:real numbers 195: 187: 183: 175: 173: 168: 164: 157: 153: 149: 145: 141: 137: 133: 129: 125: 121: 117: 113: 109: 107: 102: 98: 94: 90: 86: 70: 59:Zorn's lemma 56: 43: 35: 28: 18: 344:. For each 198:is finite. 180:cardinality 79:isomorphism 21:mathematics 1482:0768.12001 1465:1001.16500 1430:1145.12001 1384:0674.12009 1335:0739.03027 1259:References 73:is unique 1185:⊃ 955:λ 944:− 915:λ 847:λ 807:∈ 796:λ 756:∈ 743:⋅ 732:λ 719:− 701:∑ 683:λ 675:− 649:∏ 645:− 640:λ 607:λ 574:≤ 551:Λ 548:∈ 545:λ 517:λ 479:λ 415:λ 404:… 390:λ 362:∈ 357:λ 318:Λ 315:∈ 312:λ 302:λ 160:that are 132:, and so 1493:Category 1445:(1972). 1287:(1969). 1232:See also 867:. Since 624:. Write 563:and all 537:for all 202:Examples 52:closures 46:that is 1139:and if 1089:within 826:be the 822:. Let 266:integer 1480:  1463:  1453:  1428:  1418:  1382:  1372:  1333:  496:. Let 435:where 244:For a 57:Using 38:is an 1224:over 1124:is a 1115:up to 1054:over 828:ideal 783:with 335:monic 250:prime 83:fixes 81:that 75:up to 33:field 31:of a 27:, an 1451:ISBN 1416:ISBN 1370:ISBN 1283:and 280:Let 241:(π). 207:The 1478:Zbl 1461:Zbl 1426:Zbl 1380:Zbl 1331:Zbl 1323:doi 1216:of 1097:of 1081:of 1070:of 1050:of 1042:of 1001:of 879:in 830:in 340:in 248:of 194:if 186:if 182:as 91:the 77:an 42:of 19:In 1495:: 1459:. 1424:. 1378:, 1329:, 1319:38 1317:, 1296:^ 1228:. 1147:, 1058:. 1033:+1 171:. 105:. 99:an 1484:. 1467:. 1432:. 1387:. 1325:: 1226:K 1222:K 1218:K 1197:) 1194:X 1191:( 1188:K 1182:) 1176:p 1172:X 1167:( 1164:) 1161:X 1158:( 1155:K 1145:K 1141:X 1137:p 1130:K 1122:K 1107:K 1103:K 1099:K 1091:K 1087:K 1083:K 1079:K 1072:K 1068:K 1056:K 1052:S 1044:K 1040:S 1031:n 1027:K 1023:n 1018:n 1014:K 1010:K 1006:1 1003:K 999:2 996:K 992:1 989:K 975:, 972:) 969:M 966:+ 961:i 958:, 951:u 947:( 941:x 931:K 911:f 900:M 898:/ 896:R 894:= 892:1 889:K 885:I 881:R 877:M 873:R 869:I 853:j 850:, 843:r 832:R 824:I 810:R 802:j 799:, 792:r 768:] 765:x 762:[ 759:R 751:j 747:x 738:j 735:, 728:r 722:1 716:d 711:0 708:= 705:j 697:= 694:) 689:i 686:, 679:u 672:x 669:( 664:d 659:1 656:= 653:i 636:f 612:) 603:f 599:( 594:e 591:e 588:r 585:g 582:e 579:d 571:i 523:i 520:, 513:u 502:K 498:R 484:) 475:f 471:( 466:e 463:e 460:r 457:g 454:e 451:d 446:= 443:d 421:d 418:, 411:u 407:, 401:, 396:1 393:, 386:u 365:S 353:f 342:K 321:} 308:| 298:f 294:{ 291:= 288:S 269:n 262:q 254:q 239:Q 230:. 219:. 196:K 188:K 184:K 176:K 169:K 165:K 158:M 154:K 150:M 146:K 142:K 138:K 134:L 130:K 126:L 122:K 118:L 114:K 110:K 103:K 95:K 87:K 71:K 44:K 36:K

Index

mathematics
abstract algebra
field
algebraic extension
algebraically closed
closures
Zorn's lemma
ultrafilter lemma
every field has an algebraic closure
up to
isomorphism
fixes
algebraic over
cardinality
countably infinite
fundamental theorem of algebra
real numbers
complex numbers
rational numbers
algebraic numbers
transcendental extensions
finite field
prime
countably infinite
integer
monic
irreducible polynomials
ideal
splitting field
separable extension

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