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Turing degree

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2118:). The priority order on requirements is used to determine which requirement to satisfy in this case. The informal idea is that if a requirement is injured then it will eventually stop being injured after all higher priority requirements have stopped being injured, although not every priority argument has this property. An argument must be made that the overall set 766:
A great deal of research has been conducted into the structure of the Turing degrees. The following survey lists only some of the many known results. One general conclusion that can be drawn from the research is that the structure of the Turing degrees is extremely complicated.
77:
if they have the same level of unsolvability; each Turing degree is a collection of Turing equivalent sets, so that two sets are in different Turing degrees exactly when they are not Turing equivalent. Furthermore, the Turing degrees are
2122:
is r.e. and satisfies all the requirements. Priority arguments can be used to prove many facts about r.e. sets; the requirements used and the manner in which they are satisfied must be carefully chosen to produce the required result.
1901: 3524: 2090:, which is an explicit bijection of the requirements and the natural numbers. The proof proceeds inductively with one stage for each natural number; these stages can be thought of as steps of time during which the set 1835: 1759: 70:. The Turing degree of a set is a measure of how difficult it is to solve the decision problem associated with the set, that is, to determine whether an arbitrary number is in the given set. 1589: 1471: 408:. (It is common to use boldface notation for Turing degrees, in order to distinguish them from sets. When no confusion can occur, such as with , the boldface is not necessary.) 1530: 1954: 861: 755: 687: 1238: 1208: 1168: 888: 547: 503: 406: 360: 993: 650: 1840: 3152: 1927: 1323: 1299: 3574: 3457: 2788: 2720: 2641: 2611: 3545: 109:. The Turing degrees have been an area of intense research since then. Many proofs in the area make use of a proof technique known as the 3552: 3531: 1405:
can be embedded in the r.e. degrees (via an embedding that preserves suprema and infima). A particular example is shown to the right.
1254: 380:. There is a unique Turing degree containing all the computable sets, and this degree is less than every other degree. It is denoted 2822: 2766: 2683: 2585: 2532: 2520: 2498: 2801:(1993). "The theories of the T, tt, and wtt r.e. degrees: undecidability and beyond". In Univ. Nac. del Sur, Bahía Blanca (ed.). 1974: 2114:
to satisfy one requirement but doing this would cause a previously satisfied requirement to become unsatisfied (that is, to be
3602: 2004: 3597: 3266: 2738: 1803: 1688: 3027:
Lachlan, Alistair H. (1966b), "The impossibility of finding relative complements for recursively enumerable degrees",
1270: 3450: 2891: 1546: 965: 2007:). Their proofs each developed the same new method for constructing r.e. degrees, which came to be known as the 2671: 564:′ denotes the set of indices of oracle machines that halt (when given their index as input) when using 2929: 98:. It is in this sense that the Turing degree of a set corresponds to its level of algorithmic unsolvability. 3070: 3105: 3005: 1432: 1126: 3569: 3271: 2952: 2629: 2595: 146: 1484: 3150:
Post, Emil L. (1944), "Recursively enumerable sets of positive integers and their decision problems",
2815:
Recursively Enumerable Sets and Degrees: A Study of Computable Functions and Computably Generated Sets
3607: 3443: 2776: 1996: 1932: 1392: 1381: 832: 726: 658: 231: 63: 3010: 1219: 1189: 1149: 869: 528: 484: 387: 341: 3538: 3477: 3110: 2131: 1385: 2154:
be the output (binary) tape, identified with the set of cell indices where we placed 1 so far (so
3361: 3353: 3296: 3210: 3139: 3052: 3044: 2977: 2916: 2908: 2866: 2803:
Proceedings of the IX Latin American Symposium on Mathematical Logic, Part 1 (Bahía Blanca, 1992)
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studied the r.e. Turing degrees and asked whether there is any r.e. degree strictly between
1179: 1143: 971: 628: 622: 582:. The Turing jump of a degree is defined to be the degree ; this is a valid definition because 470: 35: 2636:. Studies in Logic and the Foundations of Mathematics. Vol. 143. Amsterdam: North-Holland. 2606:. Studies in Logic and the Foundations of Mathematics. Vol. 125. Amsterdam: North-Holland. 2546: 3497: 3288: 3247: 3171: 3123: 2969: 2818: 2784: 2762: 2716: 2689: 2679: 2637: 2607: 2581: 2528: 2516: 2494: 1122: 327: 3502: 3345: 3325: 3280: 3237: 3202: 3161: 3115: 3079: 3036: 3015: 2961: 2900: 2848: 2754: 2011:. The priority method is now the main technique for establishing results about r.e. sets. 506: 137: 122: 90:, then any (possibly noncomputable) procedure that correctly decides whether numbers are in 67: 31: 3308: 3259: 3183: 3135: 2989: 2862: 2651: 2621: 1896:{\displaystyle \{\mathbf {c} \mid \mathbf {a} \leq _{T}\mathbf {c} \leq _{T}\mathbf {b} \}} 3304: 3255: 3225: 3179: 3131: 3093: 3065: 2996:
Lachlan, Alistair H. (1966a), "Lower Bounds for Pairs of Recursively Enumerable Degrees",
2985: 2858: 2832: 2810: 2647: 2617: 1991:. The problem of constructing such a degree (or showing that none exist) became known as 1422: 1410: 1402: 1388: 1183: 891: 609: 550: 94:
can be effectively converted to a procedure that correctly decides whether numbers are in
3068:(1980), "Not every finite lattice is embeddable in the recursively enumerable degrees", 2950:; Post, Emil L. (1954), "The upper semi-lattice of degrees of recursive unsolvability", 1332:: The r.e. degrees are dense; between any two r.e. degrees there is a third r.e. degree. 17: 3492: 3487: 2947: 2600: 2471: 2000: 1912: 1406: 1308: 1284: 51: 2758: 2567:
Epstein, R.L.; Haas, R; Kramer, L.R. (1981). Leman, M; Schmerl, J.; Soare, R. (eds.).
2141:′=0′) can be constructed in infinitely many stages as follows. At the start of stage 3591: 3221: 3084: 2798: 2664: 2508: 716: 366: 79: 3365: 3166: 3143: 3056: 2920: 2870: 2853: 2836: 1473:
iff there is a "recursive approximation" to its characteristic function: a function
3190: 3096:(1998), "Interpretability and definability in the recursively enumerable degrees", 2708: 3507: 3466: 1017:. In fact, there is a countable family of pairwise incomparable degrees between 914:, ... of Turing degrees cannot have the least upper bound, but it always has an 801: 574: 43: 3242: 3019: 3119: 2127: 1342:: There are two r.e. degrees with no greatest lower bound in the r.e. degrees. 3329: 3292: 3251: 3175: 3127: 2973: 2904: 2693: 3316:
Thomason, S.K. (1971), "Sublattices of the recursively enumerable degrees",
2730: 2675: 1980: 897:
Every countable partially ordered set can be embedded in the Turing degrees.
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showed that the jump operator is definable in the first-order structure of
3336:
Yates, C.E.M. (1966), "A minimal pair of recursively enumerable degrees",
3269:(1977b). "First-order theory of the degrees of recursive unsolvability". 2750: 2912: 2886: 2003:
in the 1950s, who showed that these intermediate r.e. degrees do exist (
1352:: There is a pair of nonzero r.e. degrees whose greatest lower bound is 3357: 3300: 3214: 3048: 2981: 1417:): The first-order theory of the r.e. degrees in the language ⟨ 1973:"Post's problem" redirects here. For the other "Post's problem", see 3349: 3284: 3206: 3040: 2965: 968:, it can be shown there is a maximal chain of degrees of order type 1429:
Additionally, there is Shoenfield's limit lemma, a set A satisfies
1253: 2378:
from disrupting the halt; all priorities are eventually constant.
2211:, if possible (otherwise do nothing in the stage), pick the least 2110:
has been enumerated). Sometimes, a number can be enumerated into
1362:: There is no pair of r.e. degrees whose greatest lower bound is 2426:
is noncomputable since otherwise a Turing machine could halt on
3439: 3422: 3420: 3418: 2817:. Perspectives in Mathematical Logic. Berlin: Springer-Verlag. 2571:. Lecture Notes in Mathematics. Vol. 859. Springer-Verlag. 2515:. Cambridge-New York: Cambridge University Press. p. 251. 866:
There are pairs of degrees with no greatest lower bound. Thus
334:. The notation denotes the equivalence class containing a set 3435: 1421:, ≤, = ⟩ is many-one equivalent to the theory of 1384:
can be embedded into the r.e. degrees. In fact, the countable
553:, as there are pairs of degrees with no greatest lower bound. 2715:. Annals of Mathematics Studies. Princeton University Press. 2422:
steps (by recursion, this is uniformly computable from 0′).
2578:
Degrees of unsolvability. Perspectives in Mathematical Logic
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to ∞, and then set one priority ∞ cell (any will do) not in
2014:
The idea of the priority method for constructing a r.e. set
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A finite lattice that can't be embedded in the r.e. degrees.
1225: 1195: 1155: 875: 534: 490: 393: 347: 54:
measures the level of algorithmic unsolvability of the set.
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Computability, an introduction to recursive function theory
1777:-r.e. degree is a strict subclass of the class of sets of ( 2741:(1977a). "Degrees of Unsolvability: A Survey of Results". 2666:
Theory of Recursive Functions and Effective Computability
3193:(1964), "The recursively enumerable degrees are dense", 2745:. Studies in Logic and the Foundations of Mathematics. 2493:. Boca Raton, FL: Chapman & Hall/CRC. p. 424. 2094:
is enumerated. At each stage, numbers may be put into
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halt if we can do so without upsetting priorities <
2106:
requirements (that is, force them to hold once all of
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The Turing degrees are not linearly ordered by ≤
66:, where sets of natural numbers are often regarded as 1935: 1915: 1843: 1806: 1691: 1549: 1487: 1435: 1311: 1287: 1222: 1192: 1152: 974: 961:), and thus it has (non-unique) minimal upper bounds. 872: 835: 729: 661: 631: 531: 487: 390: 344: 338:. The entire collection of Turing degrees is denoted 2098:
or forever (if not injured) prevented from entering
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and finitely iterated Turing jumps of the empty set.
384:(zero) because it is the least element of the poset 3562: 3516: 2930:"The Turing degrees and their lack of linear order" 2192:) be the priority for not outputting 1 at location 2026:must satisfy. For example, to construct a r.e. set 2663: 2599: 2545:Ambos-Spies, Klaus; Fejer, Peter (20 March 2006). 2438:is nonempty, contradicting the construction since 2374:, and then set priorities to prevent machines > 1948: 1921: 1895: 1829: 1753: 1583: 1524: 1465: 1317: 1293: 1232: 1202: 1162: 987: 882: 855: 800:. Thus the order relation on the degrees is not a 749: 681: 644: 541: 497: 400: 354: 3426: 2805:. Notas Lógica Mat. Vol. 38. pp. 61–70. 1830:{\displaystyle \mathbf {a} \leq _{T}\mathbf {b} } 1754:{\displaystyle \{s\mid A_{s}(x)\neq A_{s+1}(x)\}} 369:≤ defined so that ≤ if and only if 105:and many fundamental results were established by 2539:Monographs and survey articles (graduate level) 1968: 1644:(Removing this condition yields a definition of 1414: 1125:establishes a close correspondence between the 131:will refer to a set of natural numbers. A set 62:The concept of Turing degree is fundamental in 3098:Proceedings of the London Mathematical Society 2998:Proceedings of the London Mathematical Society 3451: 3153:Bulletin of the American Mathematical Society 8: 2078:requires that the Turing machine with index 2063:requires that the oracle machine with index 1995:. This problem was solved independently by 1890: 1844: 1748: 1692: 1398: 226:are Turing equivalent. The relation ≡ 1584:{\displaystyle (A_{s})_{s\in \mathbb {N} }} 1391:can be embedded in a manner that preserves 1213: 3458: 3444: 3436: 792:is nonzero and there is no degree between 106: 3409: 3385: 3241: 3165: 3109: 3083: 3009: 2852: 2837:"Recursively enumerable sets and degrees" 2038:it is enough to satisfy the requirements 1936: 1934: 1914: 1885: 1879: 1870: 1864: 1855: 1847: 1842: 1822: 1816: 1807: 1805: 1727: 1705: 1690: 1575: 1574: 1567: 1557: 1548: 1507: 1486: 1449: 1434: 1310: 1286: 1224: 1223: 1221: 1194: 1193: 1191: 1154: 1153: 1151: 979: 973: 900:An infinite strictly increasing sequence 874: 873: 871: 845: 840: 834: 739: 734: 728: 671: 666: 660: 636: 630: 533: 532: 530: 489: 488: 486: 431:, is defined to be the union of the sets 392: 391: 389: 346: 345: 343: 86:is less than the Turing degree of a set 2885:Chong, C.T.; Yu, Liang (December 2007). 1543:-r e. if there is a family of functions 1377: 1359: 1345: 1335: 1252: 1186:. This indicates that the structure of 1139: 82:, so that if the Turing degree of a set 3397: 3378: 2928:DeAntonio, Jasper (24 September 2010). 2569:Hierarchies of sets and degrees below 0 1370:. This result is informally called the 153:when given an oracle for membership in 127:For the rest of this article, the word 2887:"Maximal Chains in the Turing Degrees" 1969:Post's problem and the priority method 616:Basic properties of the Turing degrees 101:The Turing degrees were introduced by 2086:. These requirements are put into a 1349: 1339: 1329: 1249:Recursively enumerable Turing degrees 1176:⟨ ≤, ′, = ⟩ 863:pairwise incomparable Turing degrees. 7: 3546:Computing Machinery and Intelligence 3228:(1999), "Defining the Turing jump", 1466:{\displaystyle \leq _{T}\emptyset '} 102: 3553:The Chemical Basis of Morphogenesis 2634:Classical recursion theory. Vol. II 2018:is to list a countable sequence of 1009:there is a degree strictly between 719:. The set of degrees greater than 509:. The least upper bound of degrees 3532:Systems of Logic Based on Ordinals 1960:+1)-r.e. iff both sets are weakly- 1642:with its characteristic function. 1456: 842: 814:In fact, for every nonzero degree 736: 668: 633: 25: 2082:(and no oracle) does not compute 1525:{\displaystyle g(s)=\chi _{A}(s)} 1477:such that for sufficiently large 3092:Nies, André; Shore, Richard A.; 2483:Monographs (undergraduate level) 2366:. Essentially, we make machine 1886: 1871: 1856: 1848: 1823: 1808: 1601:is a recursive approximation of 234:, which means that for all sets 3427:Epstein, Haas & Kramer 1981 3167:10.1090/S0002-9904-1944-08111-1 2854:10.1090/S0002-9904-1978-14552-2 2354:)), and set all priorities > 2130:(and hence noncomputable r.e.) 2067:does not compute 0′ from 1949:{\displaystyle {\overline {A}}} 1415:Nies, Shore & Slaman (1998) 1366:and whose least upper bound is 856:{\displaystyle 2^{\aleph _{0}}} 762:Structure of the Turing degrees 750:{\displaystyle 2^{\aleph _{0}}} 682:{\displaystyle 2^{\aleph _{0}}} 625:, that is, it contains exactly 3318:Z. Math. Logik Grundlag. Math. 1745: 1739: 1717: 1711: 1564: 1550: 1519: 1513: 1497: 1491: 1442: 1436: 1233:{\displaystyle {\mathcal {D}}} 1203:{\displaystyle {\mathcal {D}}} 1163:{\displaystyle {\mathcal {D}}} 1086:There is an infinite sequence 883:{\displaystyle {\mathcal {D}}} 542:{\displaystyle {\mathcal {D}}} 498:{\displaystyle {\mathcal {D}}} 401:{\displaystyle {\mathcal {D}}} 355:{\displaystyle {\mathcal {D}}} 1: 3230:Mathematical Research Letters 2759:10.1016/S0049-237X(08)71117-0 2743:Annals of Mathematics Studies 1975:Post's correspondence problem 1277:, but not every degree below 1273:. Every r.e. degree is below 1000:Properties involving the jump 3085:10.1016/0001-8708(80)90027-4 2446:cells for arbitrarily large 2293:. Choose any such (finite) 1941: 1638:), in particular conflating 1242:⟨ ≤, = ⟩ 1184:true second-order arithmetic 1172:⟨ ≤, = ⟩ 2580:. Berlin: Springer-Verlag. 2454:is simple because for each 1685:)=0 and the cardinality of 1670:-trial predicate": for all 1423:true first-order arithmetic 988:{\displaystyle \omega _{1}} 711:, the set of degrees below 645:{\displaystyle \aleph _{0}} 608:′, the degree of the 149:that decides membership in 3624: 3243:10.4310/mrl.1999.v6.n6.a10 2783:. North-Holland/Elsevier. 2602:Classical Recursion Theory 2547:"Degrees of Unsolvability" 1972: 1399:Lachlan & Soare (1980) 1271:recursively enumerable set 365:The Turing degrees have a 120: 3473: 3338:Journal of Symbolic Logic 3120:10.1112/S002461159800046X 2892:Journal of Symbolic Logic 2005:Friedberg–Muchnik theorem 1301:is many-one reducible to 1214:Shore & Slaman (1999) 1210:is extremely complicated. 1028:Jump inversion: a degree 966:axiom of constructibility 3330:10.1002/malq.19710170131 3020:10.1112/plms/s3-16.1.537 2781:Degrees of Unsolvability 2713:Degrees of Unsolvability 2672:Cambridge, Massachusetts 2052:for each natural number 1837:, such that the segment 1281:is r.e.. However, a set 1269:(c.e.) if it contains a 689:distinct Turing degrees. 461:}. The Turing degree of 107:Kleene & Post (1954) 27:Measure of unsolvability 18:Degrees of unsolvability 3071:Advances in Mathematics 2458:the number of priority 2442:excludes some priority 2406:such that machines < 621:Every Turing degree is 568:as an oracle. The set 330:of the relation ≡ 203:is Turing reducible to 195:is Turing reducible to 172:is Turing reducible to 48:degree of unsolvability 3064:Lachlan, Alistair H.; 2905:10.2178/jsl/1203350783 2630:Odifreddi, Piergiorgio 2596:Odifreddi, Piergiorgio 1950: 1923: 1897: 1831: 1755: 1585: 1526: 1467: 1319: 1295: 1263:recursively enumerable 1258: 1234: 1204: 1164: 1127:arithmetical hierarchy 989: 884: 857: 751: 696:the strict inequality 683: 646: 572:′ is called the 543: 499: 402: 356: 3603:Theory of computation 3570:Legacy of Alan Turing 3539:Intelligent Machinery 3525:On Computable Numbers 3272:Annals of Mathematics 3195:Annals of Mathematics 2953:Annals of Mathematics 2841:Bull. Amer. Math. Soc 2777:Shoenfield, Joseph R. 2489:Cooper, S.B. (2004). 2311:, and for every cell 1951: 1924: 1898: 1832: 1788:>1 there are two ( 1773:The class of sets of 1756: 1586: 1527: 1468: 1320: 1296: 1267:computably enumerable 1256: 1235: 1205: 1165: 1095:of degrees such that 990: 885: 858: 752: 684: 647: 544: 500: 403: 357: 230:can be seen to be an 147:oracle Turing machine 3598:Computability theory 3066:Soare, Robert Irving 2948:Kleene, Stephen Cole 2833:Soare, Robert Irving 2811:Soare, Robert Irving 2491:Computability theory 2393:iff it halts in < 2247:steps on some input 1933: 1913: 1841: 1804: 1689: 1547: 1485: 1433: 1382:distributive lattice 1309: 1285: 1220: 1190: 1150: 972: 870: 833: 727: 659: 629: 529: 525:. It is known that 485: 388: 342: 232:equivalence relation 64:computability theory 3478:Turing completeness 3412:, p. 252, 258. 3398:Chong & Yu 2007 3267:Simpson, Stephen G. 3226:Slaman, Theodore A. 3094:Slaman, Theodore A. 2576:Lerman, M. (1983). 2315:visited by machine 2239:and Turing machine 1261:A degree is called 1180:many-one equivalent 604:. A key example is 2739:Simpson, Steven G. 1946: 1919: 1893: 1827: 1751: 1581: 1522: 1463: 1393:suprema and infima 1372:nondiamond theorem 1315: 1291: 1259: 1240:with the language 1230: 1200: 1160: 1144:first-order theory 1134:Logical properties 1051:there is a degree 985: 880: 853: 829:There is a set of 822:incomparable with 818:there is a degree 747: 679: 642: 623:countably infinite 539: 495: 473:of the degrees of 398: 352: 187:are defined to be 117:Turing equivalence 36:mathematical logic 3585: 3584: 3275:. Second Series. 3222:Shore, Richard A. 3197:, Second Series, 2956:, Second Series, 2790:978-0-7204-2061-6 2722:978-0-6910-7941-7 2643:978-0-444-50205-6 2613:978-0-444-87295-1 2509:Cutland, Nigel J. 2462:cells is finite. 2102:in an attempt to 2088:priority ordering 1944: 1922:{\displaystyle A} 1792:+1)-r.e. degrees 1401:: Not all finite 1318:{\displaystyle A} 1294:{\displaystyle A} 1182:to the theory of 1005:For every degree 593:′ whenever 471:least upper bound 328:equivalence class 189:Turing equivalent 80:partially ordered 75:Turing equivalent 68:decision problems 16:(Redirected from 3615: 3503:Turing reduction 3460: 3453: 3446: 3437: 3430: 3424: 3413: 3407: 3401: 3395: 3389: 3383: 3368: 3332: 3312: 3262: 3245: 3217: 3186: 3169: 3146: 3113: 3088: 3087: 3060: 3023: 3013: 2992: 2943: 2941: 2939: 2934: 2924: 2899:(4): 1219–1227. 2874: 2856: 2847:(6): 1149–1181. 2828: 2806: 2794: 2772: 2734: 2704: 2702: 2700: 2669: 2655: 2625: 2605: 2591: 2572: 2563: 2558: 2556: 2551: 2526: 2504: 2385:is low, machine 1955: 1953: 1952: 1947: 1945: 1937: 1928: 1926: 1925: 1920: 1902: 1900: 1899: 1894: 1889: 1884: 1883: 1874: 1869: 1868: 1859: 1851: 1836: 1834: 1833: 1828: 1826: 1821: 1820: 1811: 1781:+1)-r.e. degree. 1760: 1758: 1757: 1752: 1738: 1737: 1710: 1709: 1590: 1588: 1587: 1582: 1580: 1579: 1578: 1562: 1561: 1531: 1529: 1528: 1523: 1512: 1511: 1472: 1470: 1469: 1464: 1462: 1454: 1453: 1407:L. A. Harrington 1324: 1322: 1321: 1316: 1300: 1298: 1297: 1292: 1243: 1239: 1237: 1236: 1231: 1229: 1228: 1209: 1207: 1206: 1201: 1199: 1198: 1177: 1173: 1170:in the language 1169: 1167: 1166: 1161: 1159: 1158: 1142:showed that the 1071:; such a degree 994: 992: 991: 986: 984: 983: 889: 887: 886: 881: 879: 878: 862: 860: 859: 854: 852: 851: 850: 849: 771:Order properties 756: 754: 753: 748: 746: 745: 744: 743: 707:For each degree 692:For each degree 688: 686: 685: 680: 678: 677: 676: 675: 651: 649: 648: 643: 641: 640: 548: 546: 545: 540: 538: 537: 507:join-semilattice 504: 502: 501: 496: 494: 493: 460: 445: 407: 405: 404: 399: 397: 396: 361: 359: 358: 353: 351: 350: 207:. The notation 157:. The notation 138:Turing reducible 123:Turing reduction 32:computer science 21: 3623: 3622: 3618: 3617: 3616: 3614: 3613: 3612: 3588: 3587: 3586: 3581: 3558: 3512: 3469: 3464: 3434: 3433: 3425: 3416: 3408: 3404: 3400:, p. 1224. 3396: 3392: 3384: 3380: 3375: 3350:10.2307/2269807 3335: 3315: 3285:10.2307/1971028 3265: 3220: 3207:10.2307/1970393 3189: 3149: 3091: 3063: 3041:10.2307/2270459 3026: 3011:10.1.1.106.7893 2995: 2966:10.2307/1969708 2946: 2937: 2935: 2932: 2927: 2884: 2881: 2879:Research papers 2831: 2825: 2809: 2797: 2791: 2775: 2769: 2737: 2723: 2707: 2698: 2696: 2686: 2660:Rogers, Hartley 2658: 2644: 2628: 2614: 2594: 2588: 2575: 2566: 2554: 2552: 2549: 2544: 2541: 2523: 2507: 2501: 2488: 2485: 2480: 2468: 2405: 2349: 2332: 2306: 2284: 2276: 2259: 2230: 2207:)=∞. At stage 2202: 2187: 2178: 2171: 2163: 2153: 2126:For example, a 2076: 2061: 2050: 2043: 2009:priority method 1978: 1971: 1931: 1930: 1911: 1910: 1875: 1860: 1839: 1838: 1812: 1802: 1801: 1769:-r.e. degrees: 1723: 1701: 1687: 1686: 1680: 1665: 1625: 1600: 1563: 1553: 1545: 1544: 1503: 1483: 1482: 1455: 1445: 1431: 1430: 1389:Boolean algebra 1380:: Every finite 1378:Thomason (1971) 1360:Lachlan (1966b) 1346:Lachlan (1966a) 1336:Lachlan (1966a) 1307: 1306: 1283: 1282: 1251: 1241: 1218: 1217: 1188: 1187: 1175: 1171: 1148: 1147: 1140:Simpson (1977b) 1136: 1114: 1105: 1094: 1047:For any degree 1036:if and only if 1032:is of the form 1002: 975: 970: 969: 960: 913: 906: 868: 867: 841: 836: 831: 830: 810: 778:minimal degrees 773: 764: 735: 730: 725: 724: 667: 662: 657: 656: 632: 627: 626: 618: 610:halting problem 600: 589: 586:′ ≡ 527: 526: 483: 482: 447: 432: 386: 385: 376: 340: 339: 333: 314: 303: 292: 279: 268: 256: 229: 218:indicates that 214: 168:indicates that 164: 145:if there is an 125: 119: 111:priority method 60: 52:natural numbers 28: 23: 22: 15: 12: 11: 5: 3621: 3619: 3611: 3610: 3605: 3600: 3590: 3589: 3583: 3582: 3580: 3579: 3578: 3577: 3566: 3564: 3560: 3559: 3557: 3556: 3549: 3542: 3535: 3528: 3520: 3518: 3514: 3513: 3511: 3510: 3505: 3500: 3498:Turing's proof 3495: 3493:Turing pattern 3490: 3488:Turing machine 3485: 3480: 3474: 3471: 3470: 3465: 3463: 3462: 3455: 3448: 3440: 3432: 3431: 3414: 3410:Odifreddi 1989 3402: 3390: 3386:DeAntonio 2010 3377: 3376: 3374: 3371: 3370: 3369: 3344:(2): 159–168, 3333: 3313: 3279:(1): 121–139. 3263: 3236:(6): 711–722, 3218: 3201:(2): 300–312, 3187: 3160:(5): 284–316, 3147: 3111:10.1.1.29.9588 3104:(2): 241–291, 3089: 3061: 3035:(3): 434–454, 3024: 3004:(1): 537–569, 2993: 2960:(3): 379–407, 2944: 2925: 2880: 2877: 2876: 2875: 2829: 2823: 2807: 2795: 2789: 2773: 2767: 2735: 2721: 2705: 2684: 2656: 2642: 2626: 2612: 2592: 2586: 2573: 2564: 2540: 2537: 2536: 2535: 2521: 2505: 2499: 2484: 2481: 2479: 2476: 2475: 2474: 2472:Martin measure 2467: 2464: 2401: 2397:steps on some 2345: 2327: 2301: 2280: 2272: 2255: 2226: 2200: 2183: 2176: 2167: 2159: 2149: 2074: 2059: 2048: 2041: 1993:Post's problem 1970: 1967: 1966: 1965: 1943: 1940: 1918: 1908: 1907:-r.e. degrees. 1892: 1888: 1882: 1878: 1873: 1867: 1863: 1858: 1854: 1850: 1846: 1825: 1819: 1815: 1810: 1782: 1765:Properties of 1763: 1762: 1750: 1747: 1744: 1741: 1736: 1733: 1730: 1726: 1722: 1719: 1716: 1713: 1708: 1704: 1700: 1697: 1694: 1678: 1663: 1658: 1621: 1598: 1577: 1573: 1570: 1566: 1560: 1556: 1552: 1521: 1518: 1515: 1510: 1506: 1502: 1499: 1496: 1493: 1490: 1461: 1458: 1452: 1448: 1444: 1441: 1438: 1427: 1426: 1396: 1375: 1357: 1343: 1333: 1314: 1290: 1250: 1247: 1246: 1245: 1227: 1211: 1197: 1157: 1135: 1132: 1131: 1130: 1123:Post's theorem 1120: 1110: 1100: 1090: 1084: 1045: 1026: 1001: 998: 997: 996: 982: 978: 962: 956: 911: 904: 898: 895: 877: 864: 848: 844: 839: 827: 812: 808: 805: 772: 769: 763: 760: 759: 758: 742: 738: 733: 705: 704:′ holds. 690: 674: 670: 665: 653: 639: 635: 617: 614: 598: 587: 536: 492: 395: 374: 349: 331: 320: 319: 312: 301: 290: 283: 277: 266: 260: 254: 227: 212: 162: 135:is said to be 121:Main article: 118: 115: 59: 56: 26: 24: 14: 13: 10: 9: 6: 4: 3: 2: 3620: 3609: 3606: 3604: 3601: 3599: 3596: 3595: 3593: 3576: 3573: 3572: 3571: 3568: 3567: 3565: 3561: 3554: 3550: 3547: 3543: 3540: 3536: 3533: 3529: 3526: 3522: 3521: 3519: 3515: 3509: 3506: 3504: 3501: 3499: 3496: 3494: 3491: 3489: 3486: 3484: 3483:Turing degree 3481: 3479: 3476: 3475: 3472: 3468: 3461: 3456: 3454: 3449: 3447: 3442: 3441: 3438: 3428: 3423: 3421: 3419: 3415: 3411: 3406: 3403: 3399: 3394: 3391: 3387: 3382: 3379: 3372: 3367: 3363: 3359: 3355: 3351: 3347: 3343: 3339: 3334: 3331: 3327: 3323: 3319: 3314: 3310: 3306: 3302: 3298: 3294: 3290: 3286: 3282: 3278: 3274: 3273: 3268: 3264: 3261: 3257: 3253: 3249: 3244: 3239: 3235: 3231: 3227: 3223: 3219: 3216: 3212: 3208: 3204: 3200: 3196: 3192: 3188: 3185: 3181: 3177: 3173: 3168: 3163: 3159: 3155: 3154: 3148: 3145: 3141: 3137: 3133: 3129: 3125: 3121: 3117: 3112: 3107: 3103: 3099: 3095: 3090: 3086: 3081: 3077: 3073: 3072: 3067: 3062: 3058: 3054: 3050: 3046: 3042: 3038: 3034: 3030: 3029:J. Symb. Log. 3025: 3021: 3017: 3012: 3007: 3003: 2999: 2994: 2991: 2987: 2983: 2979: 2975: 2971: 2967: 2963: 2959: 2955: 2954: 2949: 2945: 2931: 2926: 2922: 2918: 2914: 2910: 2906: 2902: 2898: 2894: 2893: 2888: 2883: 2882: 2878: 2872: 2868: 2864: 2860: 2855: 2850: 2846: 2842: 2838: 2834: 2830: 2826: 2824:3-540-15299-7 2820: 2816: 2812: 2808: 2804: 2800: 2796: 2792: 2786: 2782: 2778: 2774: 2770: 2768:9780444863881 2764: 2760: 2756: 2752: 2748: 2744: 2740: 2736: 2732: 2728: 2724: 2718: 2714: 2710: 2706: 2695: 2691: 2687: 2685:9780262680523 2681: 2677: 2673: 2668: 2667: 2661: 2657: 2653: 2649: 2645: 2639: 2635: 2631: 2627: 2623: 2619: 2615: 2609: 2604: 2603: 2597: 2593: 2589: 2587:3-540-12155-2 2583: 2579: 2574: 2570: 2565: 2562: 2548: 2543: 2542: 2538: 2534: 2533:0-521-29465-7 2530: 2524: 2522:0-521-22384-9 2518: 2514: 2510: 2506: 2502: 2500:1-58488-237-9 2496: 2492: 2487: 2486: 2482: 2477: 2473: 2470: 2469: 2465: 2463: 2461: 2457: 2453: 2449: 2445: 2441: 2437: 2433: 2429: 2425: 2421: 2417: 2413: 2410:that halt on 2409: 2404: 2400: 2396: 2392: 2388: 2384: 2379: 2377: 2373: 2369: 2365: 2361: 2357: 2353: 2348: 2344: 2340: 2336: 2330: 2326: 2322: 2318: 2314: 2310: 2304: 2300: 2296: 2292: 2288: 2283: 2279: 2275: 2271: 2267: 2263: 2258: 2254: 2250: 2246: 2243:halts in < 2242: 2238: 2234: 2229: 2225: 2222: 2218: 2214: 2210: 2206: 2199: 2195: 2191: 2186: 2182: 2179:=∅); and let 2175: 2170: 2166: 2162: 2157: 2152: 2148: 2144: 2140: 2136: 2133: 2129: 2124: 2121: 2117: 2113: 2109: 2105: 2101: 2097: 2093: 2089: 2085: 2081: 2077: 2070: 2066: 2062: 2055: 2051: 2044: 2037: 2033: 2029: 2025: 2021: 2017: 2012: 2010: 2006: 2002: 1998: 1994: 1990: 1986: 1982: 1976: 1963: 1959: 1938: 1916: 1909: 1906: 1880: 1876: 1865: 1861: 1852: 1817: 1813: 1799: 1795: 1791: 1787: 1783: 1780: 1776: 1772: 1771: 1770: 1768: 1742: 1734: 1731: 1728: 1724: 1720: 1714: 1706: 1702: 1698: 1695: 1684: 1677: 1673: 1669: 1662: 1659: 1657: 1653: 1649: 1645: 1641: 1637: 1633: 1629: 1624: 1620: 1616: 1612: 1608: 1604: 1597: 1594: 1593: 1592: 1571: 1568: 1558: 1554: 1542: 1538: 1533: 1516: 1508: 1504: 1500: 1494: 1488: 1480: 1476: 1459: 1450: 1446: 1439: 1424: 1420: 1416: 1412: 1408: 1404: 1400: 1397: 1394: 1390: 1387: 1383: 1379: 1376: 1373: 1369: 1365: 1361: 1358: 1355: 1351: 1347: 1344: 1341: 1337: 1334: 1331: 1328: 1327: 1326: 1312: 1304: 1288: 1280: 1276: 1272: 1268: 1264: 1255: 1248: 1215: 1212: 1185: 1181: 1145: 1141: 1138: 1137: 1133: 1128: 1124: 1121: 1118: 1113: 1109: 1103: 1098: 1093: 1089: 1085: 1082: 1078: 1074: 1070: 1066: 1062: 1058: 1054: 1050: 1046: 1043: 1039: 1035: 1031: 1027: 1024: 1020: 1016: 1012: 1008: 1004: 1003: 999: 980: 976: 967: 964:Assuming the 963: 959: 955: 951: 948: 944: 940: 936: 932: 928: 924: 920: 917: 910: 903: 899: 896: 893: 865: 846: 837: 828: 825: 821: 817: 813: 806: 803: 799: 795: 791: 787: 783: 779: 775: 774: 770: 768: 761: 740: 731: 722: 718: 714: 710: 706: 703: 699: 695: 691: 672: 663: 654: 637: 624: 620: 619: 615: 613: 611: 607: 603: 596: 592: 585: 581: 577: 576: 571: 567: 563: 560:the notation 559: 554: 552: 524: 520: 516: 512: 508: 480: 476: 472: 468: 464: 459: 455: 451: 444: 440: 436: 430: 426: 422: 418: 414: 411:For any sets 409: 383: 379: 372: 368: 367:partial order 363: 337: 329: 325: 324:Turing degree 317: 310: 306: 299: 295: 288: 284: 282: 275: 271: 264: 261: 259: 252: 249: 248: 247: 245: 241: 237: 233: 225: 221: 217: 210: 206: 202: 198: 194: 190: 186: 182: 177: 175: 171: 167: 160: 156: 152: 148: 144: 140: 139: 134: 130: 124: 116: 114: 112: 108: 104: 99: 97: 93: 89: 85: 81: 76: 73:Two sets are 71: 69: 65: 57: 55: 53: 49: 45: 42:(named after 41: 40:Turing degree 37: 33: 19: 3517:Publications 3482: 3405: 3393: 3388:, p. 9. 3381: 3341: 3337: 3321: 3317: 3276: 3270: 3233: 3229: 3198: 3194: 3157: 3151: 3101: 3097: 3075: 3069: 3032: 3028: 3001: 2997: 2957: 2951: 2936:. Retrieved 2896: 2890: 2844: 2840: 2814: 2802: 2780: 2746: 2742: 2731:j.ctt1b9x0r8 2712: 2697:. Retrieved 2665: 2633: 2601: 2577: 2568: 2560: 2553:. Retrieved 2512: 2490: 2459: 2455: 2451: 2447: 2443: 2439: 2435: 2431: 2427: 2423: 2419: 2415: 2411: 2407: 2402: 2398: 2394: 2390: 2386: 2382: 2381:To see that 2380: 2375: 2371: 2367: 2363: 2362:to priority 2359: 2355: 2351: 2346: 2342: 2338: 2334: 2328: 2324: 2320: 2316: 2312: 2308: 2302: 2298: 2294: 2290: 2286: 2281: 2277: 2273: 2269: 2265: 2261: 2256: 2252: 2248: 2244: 2240: 2236: 2232: 2227: 2223: 2220: 2216: 2212: 2208: 2204: 2197: 2193: 2189: 2184: 2180: 2173: 2168: 2164: 2160: 2155: 2150: 2146: 2142: 2138: 2134: 2125: 2119: 2115: 2111: 2107: 2103: 2099: 2095: 2091: 2087: 2083: 2079: 2072: 2068: 2064: 2057: 2053: 2046: 2039: 2035: 2031: 2027: 2023: 2020:requirements 2019: 2015: 2013: 2008: 1992: 1988: 1984: 1979: 1961: 1957: 1904: 1903:contains no 1797: 1793: 1789: 1785: 1778: 1774: 1766: 1764: 1761:is ≤n. 1682: 1675: 1671: 1667: 1660: 1655: 1651: 1647: 1643: 1639: 1635: 1631: 1627: 1622: 1618: 1614: 1610: 1606: 1602: 1595: 1540: 1536: 1534: 1478: 1474: 1428: 1418: 1411:T. A. Slaman 1371: 1367: 1363: 1353: 1350:Yates (1966) 1340:Yates (1966) 1330:Sacks (1964) 1302: 1278: 1274: 1266: 1262: 1260: 1116: 1111: 1107: 1101: 1096: 1091: 1087: 1080: 1079:relative to 1076: 1072: 1068: 1064: 1060: 1056: 1052: 1048: 1041: 1037: 1033: 1029: 1022: 1018: 1014: 1010: 1006: 957: 953: 949: 946: 942: 938: 934: 930: 926: 922: 918: 915: 908: 901: 823: 819: 815: 797: 793: 789: 785: 781: 780:. A degree 777: 765: 720: 712: 708: 701: 697: 693: 605: 601: 594: 590: 583: 579: 573: 569: 565: 561: 557: 556:For any set 555: 522: 518: 514: 510: 478: 474: 466: 462: 457: 453: 449: 442: 438: 434: 428: 424: 420: 416: 412: 410: 381: 377: 370: 364: 335: 323: 321: 315: 308: 304: 297: 293: 286: 280: 273: 269: 262: 257: 250: 243: 239: 235: 223: 219: 215: 208: 204: 200: 196: 192: 188: 184: 180: 178: 173: 169: 165: 158: 154: 150: 142: 136: 132: 128: 126: 110: 100: 95: 91: 87: 83: 74: 72: 61: 50:of a set of 47: 39: 29: 3608:Alan Turing 3508:Turing test 3467:Alan Turing 3324:: 273–280, 3191:Sacks, G.E. 2753:: 631–652. 2709:Sacks, G.E. 2561:Unpublished 2219:such that ∀ 2137:(low means 1605:: for some 1591:such that: 925:such that ∀ 802:dense order 575:Turing jump 517:is denoted 423:Y, written 103:Post (1944) 44:Alan Turing 3592:Categories 2478:References 2414:do so < 1609:, for any 1539:is called 1265:(r.e.) or 1075:is called 1055:such that 916:exact pair 776:There are 655:There are 452:+1 : 3575:namesakes 3293:0003-486X 3252:1073-2780 3176:0002-9904 3128:0024-6115 3106:CiteSeerX 3078:: 78–82, 3006:CiteSeerX 2974:0003-486X 2938:20 August 2799:Shore, R. 2694:933975989 2676:MIT Press 2555:20 August 2389:halts on 1997:Friedberg 1981:Emil Post 1942:¯ 1877:≤ 1862:≤ 1853:∣ 1814:≤ 1721:≠ 1699:∣ 1572:∈ 1505:χ 1457:∅ 1447:≤ 1325:is r.e.. 1115:for each 977:ω 890:is not a 843:ℵ 737:ℵ 723:has size 717:countable 669:ℵ 634:ℵ 549:is not a 179:Two sets 141:to a set 3555:" (1952) 3548:" (1950) 3541:" (1948) 3534:" (1939) 3527:" (1936) 3366:38778059 3144:16488410 3057:30992462 2921:38576214 2913:27588601 2871:29549997 2835:(1978). 2813:(1987). 2779:(1971). 2751:Elsevier 2711:(1966). 2662:(1967). 2632:(1999). 2598:(1989). 2511:(1980). 2466:See also 2337:) = min( 2056:, where 2036:0′ 2030:between 1989:0′ 1784:For all 1650:"weakly 1617:we have 1460:′ 1403:lattices 1386:atomless 1368:0′ 1303:0′ 1279:0′ 1275:0′ 1106:≤ 1069:a′ 1065:b′ 1040:≤ 1038:0′ 1034:b′ 1023:a′ 1015:a′ 521:∪ 465:⊕ 456:∈ 441:∈ 437: : 427:⊕ 272:implies 58:Overview 3563:Related 3358:2269807 3309:0432435 3301:1971028 3260:1739227 3215:1970393 3184:0010514 3136:1635141 3049:2270459 2990:0061078 2982:1969708 2863:0508451 2652:1718169 2622:0982269 2116:injured 2104:satisfy 2001:Muchnik 1666:is an " 1613:≥ 1099:′ 892:lattice 786:minimal 597:≡ 551:lattice 481:. Thus 469:is the 446:} and 373:≤ 311:≡ 300:≡ 289:≡ 276:≡ 265:≡ 253:≡ 211:≡ 161:≤ 3364:  3356:  3307:  3299:  3291:  3258:  3250:  3213:  3182:  3174:  3142:  3134:  3126:  3108:  3055:  3047:  3008:  2988:  2980:  2972:  2919:  2911:  2869:  2861:  2821:  2787:  2765:  2729:  2719:  2692:  2682:  2650:  2640:  2620:  2610:  2584:  2531:  2519:  2497:  2450:; and 2323:, set 2297:, set 2260:with ∀ 2145:, let 2128:simple 1654:-r.e." 1535:A set 326:is an 242:, and 3373:Notes 3362:S2CID 3354:JSTOR 3297:JSTOR 3211:JSTOR 3140:S2CID 3053:S2CID 3045:JSTOR 2978:JSTOR 2933:(PDF) 2917:S2CID 2909:JSTOR 2867:S2CID 2727:JSTOR 2699:6 May 2550:(PDF) 2022:that 1964:-r.e. 1956:are ( 1800:with 1648:being 1413:(see 1059:< 700:< 652:sets. 505:is a 307:then 46:) or 3289:ISSN 3248:ISSN 3172:ISSN 3124:ISSN 2970:ISSN 2940:2023 2819:ISBN 2785:ISBN 2763:ISBN 2717:ISBN 2701:2020 2690:OCLC 2680:ISBN 2638:ISBN 2608:ISBN 2582:ISBN 2557:2023 2529:ISBN 2517:ISBN 2495:ISBN 2430:iff 2215:< 2071:and 2045:and 2034:and 1999:and 1987:and 1929:and 1630:) = 1409:and 1348:and 1338:and 1305:iff 1063:and 1021:and 1013:and 941:< 933:< 796:and 513:and 477:and 421:join 419:, X 415:and 296:and 222:and 199:and 183:and 38:the 34:and 3346:doi 3326:doi 3281:doi 3277:105 3238:doi 3203:doi 3162:doi 3116:doi 3080:doi 3037:doi 3016:doi 2962:doi 2901:doi 2849:doi 2755:doi 2319:on 2132:low 1646:A 1178:is 1174:or 1146:of 1077:low 945:⇔ ∃ 788:if 784:is 715:is 578:of 285:If 246:: 191:if 129:set 30:In 3594:: 3417:^ 3360:, 3352:, 3342:31 3340:, 3322:17 3320:, 3305:MR 3303:. 3295:. 3287:. 3256:MR 3254:, 3246:, 3232:, 3224:; 3209:, 3199:80 3180:MR 3178:, 3170:, 3158:50 3156:, 3138:, 3132:MR 3130:, 3122:, 3114:, 3102:77 3100:, 3076:37 3074:, 3051:, 3043:, 3033:31 3031:, 3014:, 3000:, 2986:MR 2984:, 2976:, 2968:, 2958:59 2915:. 2907:. 2897:72 2895:. 2889:. 2865:. 2859:MR 2857:. 2845:84 2843:. 2839:. 2761:. 2749:. 2747:90 2725:. 2688:. 2678:. 2674:: 2670:. 2648:MR 2646:. 2618:MR 2616:. 2559:. 2527:; 2341:, 2331:+1 2305:+1 2289:)≥ 2235:)≠ 2196:; 2172:; 2158:=∪ 1796:, 1674:, 1532:. 1481:, 1104:+1 1067:= 921:, 907:, 612:. 448:{2 433:{2 362:. 322:A 238:, 176:. 113:. 3551:" 3544:" 3537:" 3530:" 3523:" 3459:e 3452:t 3445:v 3429:. 3348:: 3328:: 3311:. 3283:: 3240:: 3234:6 3205:: 3164:: 3118:: 3082:: 3059:. 3039:: 3022:. 3018:: 3002:3 2964:: 2942:. 2923:. 2903:: 2873:. 2851:: 2827:. 2793:. 2771:. 2757:: 2733:. 2703:. 2654:. 2624:. 2590:. 2525:. 2503:. 2460:i 2456:i 2452:X 2448:i 2444:i 2440:X 2436:X 2434:\ 2432:Y 2428:Y 2424:X 2420:i 2418:- 2416:n 2412:X 2408:i 2403:n 2399:T 2395:n 2391:X 2387:i 2383:X 2376:i 2372:i 2368:i 2364:i 2360:S 2356:i 2352:m 2350:( 2347:n 2343:P 2339:i 2335:m 2333:( 2329:n 2325:P 2321:S 2317:i 2313:m 2309:S 2307:= 2303:n 2299:T 2295:S 2291:i 2287:m 2285:( 2282:n 2278:P 2274:n 2270:T 2268:\ 2266:S 2264:∈ 2262:m 2257:n 2253:T 2251:⊇ 2249:S 2245:n 2241:i 2237:i 2233:m 2231:( 2228:n 2224:P 2221:m 2217:n 2213:i 2209:n 2205:m 2203:( 2201:0 2198:P 2194:m 2190:m 2188:( 2185:n 2181:P 2177:0 2174:T 2169:n 2165:T 2161:n 2156:X 2151:n 2147:T 2143:n 2139:X 2135:X 2120:X 2112:X 2108:X 2100:X 2096:X 2092:X 2084:X 2080:e 2075:e 2073:B 2069:X 2065:e 2060:e 2058:A 2054:e 2049:e 2047:B 2042:e 2040:A 2032:0 2028:X 2024:X 2016:X 1985:0 1977:. 1962:n 1958:n 1939:A 1917:A 1905:n 1891:} 1887:b 1881:T 1872:c 1866:T 1857:a 1849:c 1845:{ 1824:b 1818:T 1809:a 1798:b 1794:a 1790:n 1786:n 1779:n 1775:n 1767:n 1749:} 1746:) 1743:x 1740:( 1735:1 1732:+ 1729:s 1725:A 1718:) 1715:x 1712:( 1707:s 1703:A 1696:s 1693:{ 1683:x 1681:( 1679:0 1676:A 1672:x 1668:n 1664:s 1661:A 1656:) 1652:n 1640:A 1636:x 1634:( 1632:A 1628:x 1626:( 1623:s 1619:A 1615:t 1611:s 1607:t 1603:A 1599:s 1596:A 1576:N 1569:s 1565:) 1559:s 1555:A 1551:( 1541:n 1537:A 1520:) 1517:s 1514:( 1509:A 1501:= 1498:) 1495:s 1492:( 1489:g 1479:s 1475:g 1451:T 1443:] 1440:A 1437:[ 1425:. 1419:0 1395:. 1374:. 1364:0 1356:. 1354:0 1313:A 1289:A 1244:. 1226:D 1196:D 1156:D 1119:. 1117:i 1112:i 1108:a 1102:i 1097:a 1092:i 1088:a 1083:. 1081:a 1073:b 1061:b 1057:a 1053:b 1049:a 1044:. 1042:a 1030:a 1025:. 1019:a 1011:a 1007:a 995:. 981:1 958:i 954:a 952:≤ 950:e 947:i 943:d 939:e 937:∧ 935:c 931:e 929:( 927:e 923:d 919:c 912:2 909:a 905:1 902:a 894:. 876:D 847:0 838:2 826:. 824:a 820:b 816:a 811:. 809:T 804:. 798:a 794:0 790:a 782:a 757:. 741:0 732:2 721:a 713:a 709:a 702:a 698:a 694:a 673:0 664:2 638:0 606:0 602:Y 599:T 595:X 591:Y 588:T 584:X 580:X 570:X 566:X 562:X 558:X 535:D 523:b 519:a 515:b 511:a 491:D 479:Y 475:X 467:Y 463:X 458:Y 454:m 450:m 443:X 439:n 435:n 429:Y 425:X 417:Y 413:X 394:D 382:0 378:Y 375:T 371:X 348:D 336:X 332:T 318:. 316:Z 313:T 309:X 305:Z 302:T 298:Y 294:Y 291:T 287:X 281:X 278:T 274:Y 270:Y 267:T 263:X 258:X 255:T 251:X 244:Z 240:Y 236:X 228:T 224:Y 220:X 216:Y 213:T 209:X 205:X 201:Y 197:Y 193:X 185:Y 181:X 174:Y 170:X 166:Y 163:T 159:X 155:Y 151:X 143:Y 133:X 96:X 92:Y 88:Y 84:X 20:)

Index

Degrees of unsolvability
computer science
mathematical logic
Alan Turing
natural numbers
computability theory
decision problems
partially ordered
Post (1944)
Kleene & Post (1954)
Turing reduction
Turing reducible
oracle Turing machine
equivalence relation
equivalence class
partial order
least upper bound
join-semilattice
lattice
Turing jump
halting problem
countably infinite
countable
dense order
lattice
axiom of constructibility
Post's theorem
arithmetical hierarchy
Simpson (1977b)
first-order theory

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