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Cardinality

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A crude sense of cardinality, an awareness that groups of things or events compare with other groups by containing more, fewer, or the same number of instances, is observed in a variety of present-day animal species, suggesting an origin millions of years ago. Human expression of cardinality is seen
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From the 6th century BCE, the writings of Greek philosophers show hints of the cardinality of infinite sets. While they considered the notion of infinity as an endless series of actions, such as adding 1 to a number repeatedly, they did not consider the size of an infinite set of numbers to be a
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While the cardinality of a finite set is simply comparable to its number of elements, extending the notion to infinite sets usually starts with defining the notion of comparison of arbitrary sets (some of which are possibly infinite).
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years ago, with equating the size of a group with a group of recorded notches, or a representative collection of other things, such as sticks and shells. The abstraction of cardinality as a number is evident by 3000 BCE, in Sumerian
4029: 3226:. Cantor introduced the cardinal numbers, and showed—according to his bijection-based definition of size—that some infinite sets are greater than others. The smallest infinite cardinality is that of the natural numbers ( 4180: 5395: 582:, it was seen that even the infinite set of all rational numbers was not enough to describe the length of every possible line segment. Still, there was no concept of infinite sets as something that had cardinality. 2678: 3889: 3222:. Indeed, Dedekind defined an infinite set as one that can be placed into a one-to-one correspondence with a strict subset (that is, having the same size in Cantor's sense); this notion of infinity is called 3734: 3841: 4923: 3385: 4590: 3901: 3534:
of that line, but that this is equal to the number of points on a plane and, indeed, in any finite-dimensional space. These results are highly counterintuitive, because they imply that there exist
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In the above section, "cardinality" of a set was defined functionally. In other words, it was not defined as a specific object itself. However, such an object can be defined as follows.
980: 1580: 502: 3048:, a standard axiomatization of set theory; that is, it is impossible to prove the continuum hypothesis or its negation from ZFC—provided that ZFC is consistent. For more detail, see 4952: 2737: 1680: 2764: 5080: 3625: 3293: 3179: 3011: 2830: 4734: 3596:, or finite-dimensional space. These curves are not a direct proof that a line has the same number of points as a finite-dimensional space, but they can be used to obtain 2519: 2493: 2428: 2363: 2250: 1499: 1387: 1110: 3320: 3251: 3132: 3038: 2802: 2060: 2014: 1914: 1868: 212: 168: 2339: 4509: 2704: 1960: 1451: 1086: 337: 108: 3045: 448: 5687: 525: 391: 5103: 5037: 4710: 2221: 2197: 2173: 2149: 2106: 2082: 1817: 1793: 1769: 1745: 1702: 1630: 1606: 1523: 1473: 1411: 1361: 1337: 1313: 1289: 1265: 1237: 1213: 1185: 1161: 1134: 895: 871: 843: 819: 469: 419: 361: 289: 265: 72: 48: 4474: 4169:{\displaystyle {\mathfrak {c}}^{\aleph _{0}}=\left(2^{\aleph _{0}}\right)^{\aleph _{0}}=2^{{\aleph _{0}}\times {\aleph _{0}}}=2^{\aleph _{0}}={\mathfrak {c}},} 3597: 5889: 4288:{\displaystyle {\mathfrak {c}}^{\mathfrak {c}}=\left(2^{\aleph _{0}}\right)^{\mathfrak {c}}=2^{{\mathfrak {c}}\times \aleph _{0}}=2^{\mathfrak {c}}.} 4437: 8037: 6564: 4681: 8192: 5315: 5244: 3040:, i.e. there is no set whose cardinality is strictly between that of the integers and that of the real numbers. The continuum hypothesis is 6647: 5788: 5440: 5289: 2621: 608:, he demonstrated that there are sets of numbers that cannot be placed in one-to-one correspondence with the set of natural numbers, i.e. 570:, as a ratio, as long as there were a third segment, no matter how small, that could be laid end-to-end a whole number of times into both 4431: 3846: 3687: 3795: 4858: 552:
thing. The ancient Greek notion of infinity also considered the division of things into parts repeated without limit. In Euclid's
6961: 3578: 3219: 4669:{\displaystyle \left\vert C\cup D\right\vert +\left\vert C\cap D\right\vert =\left\vert C\right\vert +\left\vert D\right\vert .} 3333: 604:, a one-to-one correspondence between the elements of two sets based on a unique relationship. In 1891, with the publication of 5367: 4018:{\displaystyle {\mathfrak {c}}^{2}=\left(2^{\aleph _{0}}\right)^{2}=2^{2\times {\aleph _{0}}}=2^{\aleph _{0}}={\mathfrak {c}},} 3747: 3448: 2532: 7119: 5178: 5907: 7726: 7546: 6974: 6297: 989: 3752: 3628: 4845:{\displaystyle |A|:={\mbox{Ord}}\cap \bigcap \{\alpha \in {\mbox{Ord}}|\exists (f:A\to \alpha ):(f{\mbox{ injective}})\}} 5701: 8054: 6979: 6969: 6706: 6559: 5912: 5903: 4960: 7115: 5730: 5722: 5670: 5505: 3041: 2884: 6457: 3397: 2847: 1963: 7212: 6956: 5781: 2437: 2372: 2266: 8032: 6517: 6210: 3469: 2935: 2592: 7912: 5951: 5085:
This definition is natural since it agrees with the axiom of limitation of size which implies bijection between
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on them. There are two notions often used when referring to cardinality: one which compares sets directly using
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and others rejected the view that the whole cannot be the same size as the part. One example of this is
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The second result was first demonstrated by Cantor in 1878, but it became more apparent in 1890, when
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and the manipulation of numbers without reference to a specific group of things or events.
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between the cardinality of the reals and the cardinality of the natural numbers, that is,
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under this relation, then, consists of all those sets which have the same cardinality as
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Kurt Von Fritz (1945). "The Discovery of Incommensurability by Hippasus of Metapontum".
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However, this hypothesis can neither be proved nor disproved within the widely accepted
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that contain more elements than there are in the infinite set of natural numbers.
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Cardinal arithmetic can be used to show not only that the number of points in a
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Proceedings of the National Academy of Sciences of the United States of America
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Proceedings of the National Academy of Sciences of the United States of America
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is injective, but not surjective since 2, for instance, is not mapped to, and
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Applied Abstract Algebra, K.H. Kim, F.W. Roush, Ellis Horwood Series, 1983,
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set is designated for each equivalence class. The most common choice is the
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To better understand infinite sets, a notion of cardinality was formulated
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contains elements that do not belong to its subsets, and the supersets of
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The first of these results is apparent by considering, for instance, the
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was described as the ability to compare the length of two line segments,
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Georg Cantor (1932), Adolf Fraenkel (Lebenslauf); Ernst Zermelo (eds.),
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that has the same cardinality as the set of the natural numbers, or |
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This definition allows also obtain a cardinality of any proper class
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Cantor also showed that sets with cardinality strictly greater than
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holds for cardinality. Thus we can make the following definitions:
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Gesammelte Abhandlungen mathematischen und philosophischen Inhalts
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The Road to Reality: A Complete guide to the Laws of the Universe
3884:{\displaystyle {\mathfrak {c}}^{\mathfrak {c}}=2^{\mathfrak {c}}} 5685:
Georg Cantor (1887), "Mitteilungen zur Lehre vom Transfiniten",
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with cardinality greater than that of the natural numbers, or |
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Animals Count and Use Zero. How Far Does Their Number Sense Go?
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From this, one can show that in general, the cardinalities of
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has cardinality strictly less than the cardinality of the set
7821: 7588: 7524: 6620: 5966: 5811: 4918:{\displaystyle (x\in \bigcap Q)\iff (\forall q\in Q:x\in q)} 242:, when no confusion with other notions of size is possible. 5753: 4430:|. This holds even for infinite cardinals, and is known as 2576:. There are two ways to define the "cardinality of a set": 3380:{\displaystyle {\mathfrak {c}}=2^{\aleph _{0}}=\beth _{1}} 126:
which compares their relative size. For example, the sets
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is defined as its equivalence class under equinumerosity.
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has cardinality less than or equal to the cardinality of
5368:"Ueber eine elementare Frage der Mannigfaltigkeitslehre" 5193: 4855:
We use the intersection of a class which is defined by
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can be bijective (see picture). By a similar argument,
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The relation of having the same cardinality is called
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has cardinality strictly less than the cardinality of
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Zeitschrift fĂŒr Philosophie und philosophische Kritik
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Two sets have the same cardinality if there exists a
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Jahresbericht der Deutschen Mathematiker-Vereinigung
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include the set of all real numbers, the set of all
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One of Cantor's most important results was that the
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is a bijection. This is no longer true for infinite
600:. He examined the process of equating two sets with 718:cannot be surjective. The picture shows an example 5593:"The Independence of the Continuum Hypothesis, II" 5097: 5074: 5031: 5007: 4946: 4917: 4844: 4728: 4704: 4668: 4565: 4468: 4287: 4168: 4017: 3883: 3835: 3785: 3728: 3619: 3505: 3433: 3379: 3314: 3287: 3245: 3173: 3126: 3032: 3005: 2971: 2917: 2873: 2824: 2796: 2758: 2731: 2698: 2672: 2513: 2487: 2461: 2422: 2396: 2357: 2333: 2290: 2244: 2215: 2191: 2167: 2143: 2100: 2076: 2054: 2008: 1954: 1908: 1862: 1811: 1787: 1763: 1739: 1696: 1674: 1624: 1600: 1574: 1517: 1493: 1467: 1445: 1405: 1381: 1355: 1331: 1307: 1283: 1259: 1231: 1207: 1179: 1155: 1128: 1104: 1080: 1038: 974: 889: 865: 837: 813: 519: 496: 463: 442: 413: 385: 355: 331: 283: 259: 238:. The cardinality of a set may also be called its 206: 162: 102: 66: 42: 5220:"Cardinality | Brilliant Math & Science Wiki" 3049: 8179: 5008:{\displaystyle (x\mapsto |x|):V\to {\mbox{Ord}}} 5486: 3295:) is greater than that of the natural numbers ( 3256: 2918:{\displaystyle {\mathfrak {c}}=2^{\aleph _{0}}} 5526:"The Independence of the Continuum Hypothesis" 5350: 3558:contain elements that are not included in it. 3434:{\displaystyle 2^{\aleph _{0}}>\aleph _{0}} 2874:{\displaystyle {\mathfrak {c}}>\aleph _{0}} 7540: 5782: 2595:. This is usually taken as the definition of 2113: 1773:, if there exists an injective function from 16:Definition of the number of elements in a set 5699: 5684: 5494:; Srishti D. Chatterji; et al. (eds.), 5365: 4839: 4775: 4356:, peaches)} is a bijection between the sets 3013:is the smallest cardinal number bigger than 2462:{\displaystyle {\mathcal {P}}(\mathbb {N} )} 2406:, and it can be shown that no function from 2397:{\displaystyle {\mathcal {P}}(\mathbb {N} )} 2328: 2322: 2291:{\displaystyle {\mathcal {P}}(\mathbb {N} )} 1682:, which was established by the existence of 1033: 1001: 969: 937: 201: 183: 157: 139: 5678: 5453:(4), Leipzig: B. G. Teubner: 438–443, 4680:Definition of cardinality in class theory ( 3506:{\displaystyle 2^{\aleph _{0}}=\aleph _{1}} 2972:{\displaystyle \aleph _{1}=2^{\aleph _{0}}} 397:on each side; this is the same notation as 7547: 7533: 5974: 5789: 5775: 4884: 4880: 4736:denotes the class of all ordinal numbers. 4298: 2739:is the least cardinal number greater than 1709: 975:{\displaystyle E=\{0,2,4,6,{\text{...}}\}} 778: 655:does not have the same cardinality as its 5634: 5616: 5567: 5549: 5173:. San Francisco, CA: Dover Publications. 4480: 2507: 2481: 2452: 2416: 2387: 2351: 2281: 2238: 1663: 1575:{\displaystyle h(n)=n-(n{\text{ mod }}2)} 1487: 1375: 1098: 994: 799:(a.k.a., one-to-one correspondence) from 214:are the same size as they each contain 3 3530:is equal to the number of points in any 3322:); that is, there are more real numbers 647: 619: 497:{\displaystyle \operatorname {card} (A)} 54:has 5 elements. Thus the cardinality of 25: 5657: 4584:are related by the following equation: 3076:with cardinality less than that of the 2258:has cardinality strictly less than its 8180: 5796: 4438:Sets with cardinality of the continuum 3056:Finite, countable and uncountable sets 1245:injective or surjective function from 644:, both sets have the same cardinality. 8193:Basic concepts in infinite set theory 7528: 5770: 5590: 5523: 5390: 5388: 5313: 5194: 2836:"c"), and is also referred to as the 1970:is equivalent to the statement that 5706:, Berlin: Springer, pp. 378–439 5524:Cohen, Paul J. (December 15, 1963). 5307: 4947:{\displaystyle \bigcap \emptyset =V} 4324:= {apples, oranges, peaches}, where 3579:Hilbert's paradox of the Grand Hotel 3220:Hilbert's paradox of the Grand Hotel 986:has the same cardinality as the set 5591:Cohen, Paul J. (January 15, 1964). 4276: 4247: 4231: 4194: 4187: 4158: 4036: 4007: 3908: 3875: 3860: 3853: 3825: 3802: 3775: 3759: 3721: 3697: 3612: 3449:Cantor's first uncountability proof 3339: 3280: 3166: 2890: 2853: 2817: 2732:{\displaystyle \aleph _{\alpha +1}} 2538: 2533:Cantor's first uncountability proof 706:)} disagrees with every set in the 13: 5441:"Über das Problem der Wohlordnung" 5385: 4935: 4888: 4796: 4432:Cantor–Bernstein–Schroeder theorem 4256: 4214: 4142: 4121: 4106: 4085: 4068: 4043: 3991: 3970: 3933: 3809: 3494: 3479: 3422: 3407: 3353: 3303: 3234: 3115: 3021: 2992: 2958: 2940: 2904: 2862: 2785: 2747: 2714: 2652: 2639: 2626: 2443: 2378: 2272: 1675:{\displaystyle |E|=|\mathbb {N} |} 511: 14: 8204: 5168: 2759:{\displaystyle \aleph _{\alpha }} 615: 122:describes a relationship between 7578: 7508: 5075:{\displaystyle |P|={\mbox{Ord}}} 4712:denote a class of all sets, and 3193: 2804:), while the cardinality of the 421:may alternatively be denoted by 5711: 5651: 5584: 5517: 5480: 5413: 5396:"Infinite Sets and Cardinality" 5359: 3635:). They include, for instance: 3620:{\displaystyle {\mathfrak {c}}} 3288:{\displaystyle {\mathfrak {c}}} 3174:{\displaystyle {\mathfrak {c}}} 3006:{\displaystyle 2^{\aleph _{0}}} 2825:{\displaystyle {\mathfrak {c}}} 339:; however, if referring to the 74:is 5 or, written symbolically, 7554: 5742: 5344: 5279: 5255: 5236: 5212: 5187: 5162: 5058: 5050: 4995: 4986: 4982: 4974: 4970: 4964: 4912: 4885: 4881: 4877: 4862: 4836: 4823: 4817: 4811: 4799: 4792: 4755: 4747: 4463: 4451: 3202:breaks down when dealing with 3050:§ Cardinality of the continuum 2456: 2448: 2391: 2383: 2341:is an injective function from 2316: 2310: 2285: 2277: 2048: 2040: 2032: 2024: 2002: 1994: 1986: 1978: 1948: 1940: 1932: 1924: 1902: 1894: 1886: 1878: 1856: 1848: 1840: 1832: 1668: 1658: 1650: 1642: 1569: 1555: 1543: 1537: 1431: 1425: 1066: 1060: 491: 485: 437: 431: 379: 371: 325: 317: 309: 301: 90: 82: 1: 7469:History of mathematical logic 5155: 4487:Inclusion-exclusion principle 4364:. The cardinality of each of 3629:generalized diagonal argument 3330:. Namely, Cantor showed that 2593:initial ordinal in that class 586: 7394:Primitive recursive function 5298:Third Millennium Mathematics 5263:"Early Human Counting Tools" 4729:{\displaystyle {\mbox{Ord}}} 3269:cardinality of the continuum 3263:Cardinality of the continuum 3257:Cardinality of the continuum 2838:cardinality of the continuum 2514:{\displaystyle \mathbb {R} } 2488:{\displaystyle \mathbb {N} } 2423:{\displaystyle \mathbb {N} } 2358:{\displaystyle \mathbb {N} } 2245:{\displaystyle \mathbb {N} } 1494:{\displaystyle \mathbb {N} } 1382:{\displaystyle \mathbb {N} } 1341:. For example, the function 1105:{\displaystyle \mathbb {N} } 578:. But with the discovery of 21:Cardinality (disambiguation) 7: 5287:Third Millennium Chronology 5285:Duncan J. Melville (2003). 5108: 3546:that have the same size as 3315:{\displaystyle \aleph _{0}} 3246:{\displaystyle \aleph _{0}} 3206:. In the late 19th century 3127:{\displaystyle \aleph _{0}} 3033:{\displaystyle \aleph _{0}} 2840:. Cantor showed, using the 2797:{\displaystyle \aleph _{0}} 2611:, the cardinalities of the 2055:{\displaystyle |B|\leq |A|} 2009:{\displaystyle |A|\leq |B|} 1909:{\displaystyle |B|\leq |A|} 1863:{\displaystyle |A|\leq |B|} 907:. Such sets are said to be 207:{\displaystyle B=\{2,4,6\}} 163:{\displaystyle A=\{1,2,3\}} 10: 8209: 8038:von Neumann–Bernays–Gödel 6458:Schröder–Bernstein theorem 6185:Monadic predicate calculus 5844:Foundations of mathematics 4484: 3891:can be demonstrated using 3641:the set of all subsets of 3445:Cantor's diagonal argument 3260: 3198:Our intuition gained from 2542: 2529:Cantor's diagonal argument 2334:{\displaystyle g(n)=\{n\}} 1964:Schröder–Bernstein theorem 606:Cantor's diagonal argument 530: 18: 8102: 8065: 7977: 7867: 7839:One-to-one correspondence 7755: 7696: 7587: 7576: 7562: 7504: 7491:Philosophy of mathematics 7440:Automated theorem proving 7422: 7317: 7149: 7042: 6894: 6611: 6587: 6565:Von Neumann–Bernays–Gödel 6510: 6404: 6308: 6206: 6197: 6124: 6059: 5965: 5887: 5804: 5497:GrundzĂŒge der Mengenlehre 5353:The Annals of Mathematics 5323:Texas A&M Mathematics 5316:"The History of Infinity" 3567:one-to-one correspondence 2580:The cardinality of a set 234:, and another which uses 3523:, if ZFC is consistent. 3459:states that there is no 624:Bijective function from 7141:Self-verifying theories 6962:Tarski's axiomatization 5913:Tarski's undefinability 5908:incompleteness theorems 5513:Original edition (1914) 5302:St. Lawrence University 4299:Examples and properties 2769:The cardinality of the 2699:{\displaystyle \alpha } 1955:{\displaystyle |A|=|B|} 1446:{\displaystyle g(n)=4n} 1081:{\displaystyle f(n)=2n} 363:, it is simply denoted 332:{\displaystyle |A|=|B|} 7797:Constructible universe 7624:Constructibility (V=L) 7515:Mathematics portal 7126:Proof of impossibility 6774:propositional variable 6084:Propositional calculus 5551:10.1073/pnas.50.6.1143 5400:Mathematics LibreTexts 5314:Allen, Donald (2003). 5242:Cepelewicz, Jordana 5105:and any proper class. 5099: 5076: 5033: 5009: 4948: 4919: 4846: 4730: 4706: 4670: 4567: 4481:Union and intersection 4470: 4289: 4170: 4019: 3885: 3837: 3787: 3730: 3681:Both have cardinality 3668:of all functions from 3621: 3507: 3435: 3381: 3316: 3289: 3247: 3175: 3128: 3034: 3007: 2973: 2919: 2875: 2826: 2798: 2760: 2733: 2700: 2674: 2515: 2489: 2463: 2424: 2398: 2359: 2335: 2292: 2246: 2217: 2193: 2169: 2145: 2102: 2078: 2056: 2010: 1956: 1910: 1864: 1813: 1789: 1765: 1741: 1698: 1676: 1626: 1602: 1576: 1519: 1495: 1469: 1447: 1407: 1383: 1357: 1333: 1309: 1285: 1261: 1233: 1209: 1193:bijection exists from 1181: 1157: 1130: 1106: 1082: 1040: 976: 891: 867: 839: 815: 771: 722:and the corresponding 666:): For every function 645: 640:is a proper subset of 521: 498: 465: 444: 415: 387: 357: 333: 285: 261: 208: 164: 111: 104: 68: 44: 8020:Principia Mathematica 7854:Transfinite induction 7713:(i.e. set difference) 7384:Kolmogorov complexity 7337:Computably enumerable 7237:Model complete theory 7029:Principia Mathematica 6089:Propositional formula 5918:Banach–Tarski paradox 5618:10.1073/pnas.51.1.105 5446:Mathematische Annalen 5366:Georg Cantor (1891). 5100: 5077: 5034: 5010: 4949: 4920: 4847: 4731: 4707: 4671: 4568: 4471: 4383:|, then there exists 4336:are distinct, then | 4290: 4171: 4020: 3886: 3838: 3788: 3731: 3622: 3508: 3436: 3382: 3326:than natural numbers 3317: 3290: 3248: 3176: 3129: 3035: 3008: 2974: 2920: 2876: 2827: 2799: 2761: 2734: 2701: 2675: 2516: 2490: 2464: 2425: 2399: 2360: 2336: 2293: 2247: 2228:For example, the set 2218: 2194: 2170: 2146: 2103: 2079: 2057: 2011: 1957: 1911: 1865: 1814: 1790: 1766: 1742: 1699: 1677: 1627: 1603: 1577: 1520: 1496: 1470: 1448: 1408: 1384: 1358: 1334: 1310: 1286: 1262: 1234: 1210: 1182: 1158: 1131: 1107: 1083: 1050:, since the function 1041: 977: 924:For example, the set 892: 868: 840: 816: 651: 623: 522: 499: 466: 445: 416: 388: 358: 343:of an individual set 334: 286: 262: 209: 165: 105: 103:{\displaystyle |S|=5} 69: 45: 29: 8094:Burali-Forti paradox 7849:Set-builder notation 7802:Continuum hypothesis 7742:Symmetric difference 7332:Church–Turing thesis 7319:Computability theory 6528:continuum hypothesis 6046:Square of opposition 5904:Gödel's completeness 5421:Friedrich M. Hartogs 5171:Set Theory and Logic 5150:Pigeonhole principle 5089: 5046: 5023: 4961: 4929: 4859: 4743: 4716: 4696: 4591: 4510: 4448: 4181: 4030: 3902: 3847: 3796: 3753: 3688: 3607: 3590:space-filling curves 3521:axiomatic set theory 3470: 3457:continuum hypothesis 3398: 3334: 3299: 3275: 3230: 3161: 3111: 3017: 2983: 2936: 2930:continuum hypothesis 2885: 2848: 2812: 2781: 2743: 2710: 2690: 2622: 2601:axiomatic set theory 2558:equivalence relation 2503: 2477: 2438: 2412: 2373: 2347: 2304: 2267: 2234: 2207: 2183: 2159: 2135: 2114:Definition 3: | 2092: 2068: 2020: 1974: 1920: 1874: 1828: 1803: 1779: 1755: 1731: 1710:Definition 2: | 1688: 1638: 1616: 1592: 1531: 1509: 1483: 1459: 1419: 1397: 1371: 1347: 1323: 1299: 1275: 1251: 1223: 1199: 1171: 1147: 1120: 1094: 1088:is a bijection from 1054: 990: 928: 881: 857: 829: 805: 779:Definition 1: | 596:, the originator of 508: 476: 455: 443:{\displaystyle n(A)} 425: 405: 367: 347: 297: 275: 251: 174: 130: 78: 58: 34: 19:For other uses, see 8055:Tarski–Grothendieck 7486:Mathematical object 7377:P versus NP problem 7342:Computable function 7136:Reverse mathematics 7062:Logical consequence 6939:primitive recursive 6934:elementary function 6707:Free/bound variable 6560:Tarski–Grothendieck 6079:Logical connectives 6009:Logical equivalence 5859:Logical consequence 5725:(student edition), 5609:1964PNAS...51..105C 5542:1963PNAS...50.1143C 3893:cardinal arithmetic 3748:cardinal equalities 3565:, which provides a 3542:of an infinite set 3088:|, is said to be a 2881:. We can show that 520:{\displaystyle \#A} 386:{\displaystyle |A|} 7644:Limitation of size 7284:Transfer principle 7247:Semantics of logic 7232:Categorical theory 7208:Non-standard model 6722:Logical connective 5849:Information theory 5798:Mathematical logic 5708:Here: p.413 bottom 5459:10.1007/bf01458215 5292:2018-07-07 at the 5196:Weisstein, Eric W. 5095: 5072: 5070: 5029: 5005: 5003: 4944: 4915: 4842: 4834: 4789: 4767: 4726: 4724: 4702: 4666: 4563: 4466: 4442:irrational numbers 4285: 4166: 4015: 3881: 3833: 3783: 3726: 3617: 3503: 3431: 3377: 3312: 3285: 3243: 3171: 3136:countably infinite 3134:, is said to be a 3124: 3030: 3003: 2969: 2915: 2871: 2822: 2794: 2756: 2729: 2696: 2670: 2527:. For proofs, see 2511: 2485: 2459: 2420: 2394: 2355: 2331: 2288: 2242: 2213: 2189: 2165: 2141: 2120:| < | 2098: 2074: 2052: 2006: 1952: 1906: 1860: 1809: 1785: 1761: 1737: 1694: 1672: 1622: 1598: 1572: 1515: 1491: 1465: 1443: 1403: 1379: 1353: 1329: 1305: 1281: 1257: 1229: 1205: 1177: 1153: 1126: 1102: 1078: 1036: 972: 887: 863: 835: 811: 772: 646: 580:irrational numbers 517: 494: 461: 440: 411: 383: 353: 329: 281: 257: 204: 160: 112: 100: 64: 40: 8175: 8174: 8084:Russell's paradox 8033:Zermelo–Fraenkel 7934:Dedekind-infinite 7807:Diagonal argument 7706:Cartesian product 7570:Set (mathematics) 7522: 7521: 7454:Abstract category 7257:Theories of truth 7067:Rule of inference 7057:Natural deduction 7038: 7037: 6583: 6582: 6288:Cartesian product 6193: 6192: 6099:Many-valued logic 6074:Boolean functions 5957:Russell's paradox 5932:diagonal argument 5829:First-order logic 5733:(library edition) 5665:, Vintage Books, 5332:on August 1, 2020 5199:"Cardinal Number" 5180:978-0-486-63829-4 5169:Stoll, Robert R. 5098:{\displaystyle V} 5069: 5032:{\displaystyle P} 5002: 4833: 4788: 4766: 4723: 4705:{\displaystyle V} 4444:and the interval 3224:Dedekind infinite 3185:|, is said to be 3153:|, for example | 3066:law of trichotomy 2842:diagonal argument 2566:equivalence class 2564:of all sets. The 2556:, and this is an 2216:{\displaystyle B} 2192:{\displaystyle A} 2168:{\displaystyle B} 2144:{\displaystyle A} 2101:{\displaystyle B} 2077:{\displaystyle A} 1962:(a fact known as 1812:{\displaystyle B} 1788:{\displaystyle A} 1764:{\displaystyle B} 1740:{\displaystyle A} 1697:{\displaystyle f} 1625:{\displaystyle h} 1601:{\displaystyle g} 1564: 1518:{\displaystyle E} 1468:{\displaystyle h} 1406:{\displaystyle E} 1356:{\displaystyle g} 1332:{\displaystyle B} 1308:{\displaystyle A} 1284:{\displaystyle B} 1260:{\displaystyle A} 1232:{\displaystyle B} 1208:{\displaystyle A} 1180:{\displaystyle B} 1156:{\displaystyle A} 1129:{\displaystyle E} 1031: 967: 890:{\displaystyle B} 866:{\displaystyle A} 838:{\displaystyle B} 814:{\displaystyle A} 464:{\displaystyle A} 414:{\displaystyle A} 356:{\displaystyle A} 284:{\displaystyle B} 260:{\displaystyle A} 67:{\displaystyle S} 43:{\displaystyle S} 8200: 8188:Cardinal numbers 8157:Bertrand Russell 8147:John von Neumann 8132:Abraham Fraenkel 8127:Richard Dedekind 8089:Suslin's problem 8000:Cantor's theorem 7717:De Morgan's laws 7582: 7549: 7542: 7535: 7526: 7525: 7513: 7512: 7464:History of logic 7459:Category of sets 7352:Decision problem 7131:Ordinal analysis 7072:Sequent calculus 6970:Boolean algebras 6910: 6909: 6884: 6855:logical/constant 6609: 6608: 6595: 6518:Zermelo–Fraenkel 6269:Set operations: 6204: 6203: 6141: 5972: 5971: 5952:Löwenheim–Skolem 5839:Formal semantics 5791: 5784: 5777: 5768: 5767: 5761: 5746: 5734: 5715: 5709: 5707: 5696: 5682: 5676: 5675: 5655: 5649: 5648: 5638: 5620: 5588: 5582: 5581: 5571: 5553: 5536:(6): 1143–1148. 5521: 5515: 5510: 5492:Egbert Brieskorn 5484: 5478: 5477: 5429:Walther von Dyck 5417: 5411: 5410: 5408: 5407: 5392: 5383: 5382: 5372: 5363: 5357: 5356: 5348: 5342: 5341: 5339: 5337: 5331: 5325:. Archived from 5320: 5311: 5305: 5283: 5277: 5276: 5274: 5273: 5259: 5253: 5252:, August 9, 2021 5240: 5234: 5233: 5231: 5230: 5216: 5210: 5209: 5208: 5191: 5185: 5184: 5166: 5130:Cantor's theorem 5125:Cantor's paradox 5104: 5102: 5101: 5096: 5081: 5079: 5078: 5073: 5071: 5067: 5061: 5053: 5039:, in particular 5038: 5036: 5035: 5030: 5014: 5012: 5011: 5006: 5004: 5000: 4985: 4977: 4954:. In this case 4953: 4951: 4950: 4945: 4924: 4922: 4921: 4916: 4851: 4849: 4848: 4843: 4835: 4831: 4795: 4790: 4786: 4768: 4764: 4758: 4750: 4735: 4733: 4732: 4727: 4725: 4721: 4711: 4709: 4708: 4703: 4675: 4673: 4672: 4667: 4662: 4648: 4634: 4630: 4612: 4608: 4572: 4570: 4569: 4564: 4559: 4545: 4531: 4527: 4475: 4473: 4472: 4469:{\displaystyle } 4467: 4294: 4292: 4291: 4286: 4281: 4280: 4279: 4266: 4265: 4264: 4263: 4251: 4250: 4236: 4235: 4234: 4228: 4224: 4223: 4222: 4221: 4199: 4198: 4197: 4191: 4190: 4175: 4173: 4172: 4167: 4162: 4161: 4152: 4151: 4150: 4149: 4132: 4131: 4130: 4129: 4128: 4115: 4114: 4113: 4095: 4094: 4093: 4092: 4082: 4078: 4077: 4076: 4075: 4053: 4052: 4051: 4050: 4040: 4039: 4024: 4022: 4021: 4016: 4011: 4010: 4001: 4000: 3999: 3998: 3981: 3980: 3979: 3978: 3977: 3953: 3952: 3947: 3943: 3942: 3941: 3940: 3918: 3917: 3912: 3911: 3890: 3888: 3887: 3882: 3880: 3879: 3878: 3865: 3864: 3863: 3857: 3856: 3842: 3840: 3839: 3834: 3829: 3828: 3819: 3818: 3817: 3816: 3806: 3805: 3792: 3790: 3789: 3784: 3779: 3778: 3769: 3768: 3763: 3762: 3735: 3733: 3732: 3727: 3725: 3724: 3715: 3714: 3702: 3701: 3700: 3626: 3624: 3623: 3618: 3616: 3615: 3563:tangent function 3540:proper supersets 3528:real number line 3512: 3510: 3509: 3504: 3502: 3501: 3489: 3488: 3487: 3486: 3440: 3438: 3437: 3432: 3430: 3429: 3417: 3416: 3415: 3414: 3386: 3384: 3383: 3378: 3376: 3375: 3363: 3362: 3361: 3360: 3343: 3342: 3321: 3319: 3318: 3313: 3311: 3310: 3294: 3292: 3291: 3286: 3284: 3283: 3252: 3250: 3249: 3244: 3242: 3241: 3216:Richard Dedekind 3180: 3178: 3177: 3172: 3170: 3169: 3133: 3131: 3130: 3125: 3123: 3122: 3039: 3037: 3036: 3031: 3029: 3028: 3012: 3010: 3009: 3004: 3002: 3001: 3000: 2999: 2978: 2976: 2975: 2970: 2968: 2967: 2966: 2965: 2948: 2947: 2924: 2922: 2921: 2916: 2914: 2913: 2912: 2911: 2894: 2893: 2880: 2878: 2877: 2872: 2870: 2869: 2857: 2856: 2831: 2829: 2828: 2823: 2821: 2820: 2803: 2801: 2800: 2795: 2793: 2792: 2765: 2763: 2762: 2757: 2755: 2754: 2738: 2736: 2735: 2730: 2728: 2727: 2705: 2703: 2702: 2697: 2679: 2677: 2676: 2671: 2660: 2659: 2647: 2646: 2634: 2633: 2539:Cardinal numbers 2522: 2520: 2518: 2517: 2512: 2510: 2496: 2494: 2492: 2491: 2486: 2484: 2470: 2468: 2466: 2465: 2460: 2455: 2447: 2446: 2431: 2429: 2427: 2426: 2421: 2419: 2405: 2403: 2401: 2400: 2395: 2390: 2382: 2381: 2366: 2364: 2362: 2361: 2356: 2354: 2340: 2338: 2337: 2332: 2299: 2297: 2295: 2294: 2289: 2284: 2276: 2275: 2253: 2251: 2249: 2248: 2243: 2241: 2224: 2222: 2220: 2219: 2214: 2200: 2198: 2196: 2195: 2190: 2176: 2174: 2172: 2171: 2166: 2152: 2150: 2148: 2147: 2142: 2125: 2119: 2109: 2107: 2105: 2104: 2099: 2085: 2083: 2081: 2080: 2075: 2061: 2059: 2058: 2053: 2051: 2043: 2035: 2027: 2015: 2013: 2012: 2007: 2005: 1997: 1989: 1981: 1961: 1959: 1958: 1953: 1951: 1943: 1935: 1927: 1915: 1913: 1912: 1907: 1905: 1897: 1889: 1881: 1869: 1867: 1866: 1861: 1859: 1851: 1843: 1835: 1820: 1818: 1816: 1815: 1810: 1796: 1794: 1792: 1791: 1786: 1772: 1770: 1768: 1767: 1762: 1748: 1746: 1744: 1743: 1738: 1721: 1715: 1705: 1703: 1701: 1700: 1695: 1681: 1679: 1678: 1673: 1671: 1666: 1661: 1653: 1645: 1633: 1631: 1629: 1628: 1623: 1609: 1607: 1605: 1604: 1599: 1584:modulo operation 1581: 1579: 1578: 1573: 1565: 1562: 1526: 1524: 1522: 1521: 1516: 1502: 1500: 1498: 1497: 1492: 1490: 1476: 1474: 1472: 1471: 1466: 1452: 1450: 1449: 1444: 1414: 1412: 1410: 1409: 1404: 1390: 1388: 1386: 1385: 1380: 1378: 1364: 1362: 1360: 1359: 1354: 1340: 1338: 1336: 1335: 1330: 1316: 1314: 1312: 1311: 1306: 1292: 1290: 1288: 1287: 1282: 1268: 1266: 1264: 1263: 1258: 1240: 1238: 1236: 1235: 1230: 1216: 1214: 1212: 1211: 1206: 1188: 1186: 1184: 1183: 1178: 1164: 1162: 1160: 1159: 1154: 1141:For finite sets 1137: 1135: 1133: 1132: 1127: 1113: 1111: 1109: 1108: 1103: 1101: 1087: 1085: 1084: 1079: 1045: 1043: 1042: 1037: 1032: 1029: 997: 982:of non-negative 981: 979: 978: 973: 968: 965: 898: 896: 894: 893: 888: 874: 872: 870: 869: 864: 846: 844: 842: 841: 836: 822: 820: 818: 817: 812: 790: 784: 753: 731: 610:uncountable sets 591: 588: 560:commensurability 542: 541: 526: 524: 523: 518: 503: 501: 500: 495: 471: 470: 468: 467: 462: 449: 447: 446: 441: 420: 418: 417: 412: 392: 390: 389: 384: 382: 374: 362: 360: 359: 354: 338: 336: 335: 330: 328: 320: 312: 304: 292: 290: 288: 287: 282: 268: 266: 264: 263: 258: 236:cardinal numbers 213: 211: 210: 205: 169: 167: 166: 161: 109: 107: 106: 101: 93: 85: 73: 71: 70: 65: 49: 47: 46: 41: 8208: 8207: 8203: 8202: 8201: 8199: 8198: 8197: 8178: 8177: 8176: 8171: 8098: 8077: 8061: 8026:New Foundations 7973: 7863: 7782:Cardinal number 7765: 7751: 7692: 7583: 7574: 7558: 7553: 7523: 7518: 7507: 7500: 7445:Category theory 7435:Algebraic logic 7418: 7389:Lambda calculus 7327:Church encoding 7313: 7289:Truth predicate 7145: 7111:Complete theory 7034: 6903: 6899: 6895: 6890: 6882: 6602: and  6598: 6593: 6579: 6555:New Foundations 6523:axiom of choice 6506: 6468:Gödel numbering 6408: and  6400: 6304: 6189: 6139: 6120: 6069:Boolean algebra 6055: 6019:Equiconsistency 5984:Classical logic 5961: 5942:Halting problem 5930: and  5906: and  5894: and  5893: 5888:Theorems ( 5883: 5800: 5795: 5765: 5764: 5747: 5743: 5738: 5737: 5716: 5712: 5697: 5683: 5679: 5673: 5656: 5652: 5589: 5585: 5522: 5518: 5508: 5488:Felix Hausdorff 5485: 5481: 5437:Otto Blumenthal 5418: 5414: 5405: 5403: 5394: 5393: 5386: 5370: 5364: 5360: 5349: 5345: 5335: 5333: 5329: 5318: 5312: 5308: 5294:Wayback Machine 5284: 5280: 5271: 5269: 5261: 5260: 5256: 5241: 5237: 5228: 5226: 5218: 5217: 5213: 5192: 5188: 5181: 5167: 5163: 5158: 5111: 5090: 5087: 5086: 5065: 5057: 5049: 5047: 5044: 5043: 5024: 5021: 5020: 4998: 4981: 4973: 4962: 4959: 4958: 4930: 4927: 4926: 4860: 4857: 4856: 4832: injective 4829: 4791: 4784: 4762: 4754: 4746: 4744: 4741: 4740: 4719: 4717: 4714: 4713: 4697: 4694: 4693: 4690: 4652: 4638: 4620: 4616: 4598: 4594: 4592: 4589: 4588: 4549: 4535: 4517: 4513: 4511: 4508: 4507: 4489: 4483: 4449: 4446: 4445: 4301: 4275: 4274: 4270: 4259: 4255: 4246: 4245: 4244: 4240: 4230: 4229: 4217: 4213: 4212: 4208: 4204: 4203: 4193: 4192: 4186: 4185: 4184: 4182: 4179: 4178: 4157: 4156: 4145: 4141: 4140: 4136: 4124: 4120: 4119: 4109: 4105: 4104: 4103: 4099: 4088: 4084: 4083: 4071: 4067: 4066: 4062: 4058: 4057: 4046: 4042: 4041: 4035: 4034: 4033: 4031: 4028: 4027: 4006: 4005: 3994: 3990: 3989: 3985: 3973: 3969: 3968: 3961: 3957: 3948: 3936: 3932: 3931: 3927: 3923: 3922: 3913: 3907: 3906: 3905: 3903: 3900: 3899: 3874: 3873: 3869: 3859: 3858: 3852: 3851: 3850: 3848: 3845: 3844: 3824: 3823: 3812: 3808: 3807: 3801: 3800: 3799: 3797: 3794: 3793: 3774: 3773: 3764: 3758: 3757: 3756: 3754: 3751: 3750: 3720: 3719: 3710: 3706: 3696: 3695: 3691: 3689: 3686: 3685: 3627:exist (see his 3611: 3610: 3608: 3605: 3604: 3588:introduced the 3497: 3493: 3482: 3478: 3477: 3473: 3471: 3468: 3467: 3461:cardinal number 3425: 3421: 3410: 3406: 3405: 3401: 3399: 3396: 3395: 3371: 3367: 3356: 3352: 3351: 3347: 3338: 3337: 3335: 3332: 3331: 3306: 3302: 3300: 3297: 3296: 3279: 3278: 3276: 3273: 3272: 3265: 3259: 3237: 3233: 3231: 3228: 3227: 3196: 3165: 3164: 3162: 3159: 3158: 3118: 3114: 3112: 3109: 3108: 3078:natural numbers 3062:axiom of choice 3058: 3024: 3020: 3018: 3015: 3014: 2995: 2991: 2990: 2986: 2984: 2981: 2980: 2961: 2957: 2956: 2952: 2943: 2939: 2937: 2934: 2933: 2907: 2903: 2902: 2898: 2889: 2888: 2886: 2883: 2882: 2865: 2861: 2852: 2851: 2849: 2846: 2845: 2832:" (a lowercase 2816: 2815: 2813: 2810: 2809: 2808:is denoted by " 2788: 2784: 2782: 2779: 2778: 2771:natural numbers 2750: 2746: 2744: 2741: 2740: 2717: 2713: 2711: 2708: 2707: 2691: 2688: 2687: 2655: 2651: 2642: 2638: 2629: 2625: 2623: 2620: 2619: 2609:axiom of choice 2597:cardinal number 2547: 2545:Cardinal number 2541: 2506: 2504: 2501: 2500: 2498: 2480: 2478: 2475: 2474: 2472: 2451: 2442: 2441: 2439: 2436: 2435: 2433: 2415: 2413: 2410: 2409: 2407: 2386: 2377: 2376: 2374: 2371: 2370: 2368: 2350: 2348: 2345: 2344: 2342: 2305: 2302: 2301: 2280: 2271: 2270: 2268: 2265: 2264: 2262: 2256:natural numbers 2237: 2235: 2232: 2231: 2229: 2208: 2205: 2204: 2202: 2184: 2181: 2180: 2178: 2160: 2157: 2156: 2154: 2136: 2133: 2132: 2130: 2128: 2121: 2115: 2093: 2090: 2089: 2087: 2069: 2066: 2065: 2063: 2047: 2039: 2031: 2023: 2021: 2018: 2017: 2001: 1993: 1985: 1977: 1975: 1972: 1971: 1968:axiom of choice 1947: 1939: 1931: 1923: 1921: 1918: 1917: 1901: 1893: 1885: 1877: 1875: 1872: 1871: 1855: 1847: 1839: 1831: 1829: 1826: 1825: 1804: 1801: 1800: 1798: 1780: 1777: 1776: 1774: 1756: 1753: 1752: 1750: 1732: 1729: 1728: 1726: 1724: 1717: 1716:| ≀ | 1711: 1689: 1686: 1685: 1683: 1667: 1662: 1657: 1649: 1641: 1639: 1636: 1635: 1617: 1614: 1613: 1611: 1593: 1590: 1589: 1587: 1563: mod  1561: 1532: 1529: 1528: 1510: 1507: 1506: 1504: 1486: 1484: 1481: 1480: 1478: 1460: 1457: 1456: 1454: 1420: 1417: 1416: 1398: 1395: 1394: 1392: 1374: 1372: 1369: 1368: 1366: 1348: 1345: 1344: 1342: 1324: 1321: 1320: 1318: 1300: 1297: 1296: 1294: 1276: 1273: 1272: 1270: 1252: 1249: 1248: 1246: 1224: 1221: 1220: 1218: 1200: 1197: 1196: 1194: 1172: 1169: 1168: 1166: 1148: 1145: 1144: 1142: 1138:(see picture). 1121: 1118: 1117: 1115: 1097: 1095: 1092: 1091: 1089: 1055: 1052: 1051: 1048:natural numbers 1028: 993: 991: 988: 987: 964: 929: 926: 925: 882: 879: 878: 876: 858: 855: 854: 852: 830: 827: 826: 824: 806: 803: 802: 800: 793: 786: 785:| = | 780: 749: 727: 618: 589: 539: 537: 533: 509: 506: 505: 477: 474: 473: 456: 453: 452: 451: 426: 423: 422: 406: 403: 402: 378: 370: 368: 365: 364: 348: 345: 344: 341:cardinal number 324: 316: 308: 300: 298: 295: 294: 276: 273: 272: 270: 252: 249: 248: 246: 245:When two sets, 175: 172: 171: 131: 128: 127: 89: 81: 79: 76: 75: 59: 56: 55: 52:Platonic solids 35: 32: 31: 24: 17: 12: 11: 5: 8206: 8196: 8195: 8190: 8173: 8172: 8170: 8169: 8164: 8162:Thoralf Skolem 8159: 8154: 8149: 8144: 8139: 8134: 8129: 8124: 8119: 8114: 8108: 8106: 8100: 8099: 8097: 8096: 8091: 8086: 8080: 8078: 8076: 8075: 8072: 8066: 8063: 8062: 8060: 8059: 8058: 8057: 8052: 8047: 8046: 8045: 8030: 8029: 8028: 8016: 8015: 8014: 8003: 8002: 7997: 7992: 7987: 7981: 7979: 7975: 7974: 7972: 7971: 7966: 7961: 7956: 7947: 7942: 7937: 7927: 7922: 7921: 7920: 7915: 7910: 7900: 7890: 7885: 7880: 7874: 7872: 7865: 7864: 7862: 7861: 7856: 7851: 7846: 7844:Ordinal number 7841: 7836: 7831: 7826: 7825: 7824: 7819: 7809: 7804: 7799: 7794: 7789: 7779: 7774: 7768: 7766: 7764: 7763: 7760: 7756: 7753: 7752: 7750: 7749: 7744: 7739: 7734: 7729: 7724: 7722:Disjoint union 7719: 7714: 7708: 7702: 7700: 7694: 7693: 7691: 7690: 7689: 7688: 7683: 7672: 7671: 7669:Martin's axiom 7666: 7661: 7656: 7651: 7646: 7641: 7636: 7634:Extensionality 7631: 7626: 7621: 7620: 7619: 7614: 7609: 7599: 7593: 7591: 7585: 7584: 7577: 7575: 7573: 7572: 7566: 7564: 7560: 7559: 7552: 7551: 7544: 7537: 7529: 7520: 7519: 7505: 7502: 7501: 7499: 7498: 7493: 7488: 7483: 7478: 7477: 7476: 7466: 7461: 7456: 7447: 7442: 7437: 7432: 7430:Abstract logic 7426: 7424: 7420: 7419: 7417: 7416: 7411: 7409:Turing machine 7406: 7401: 7396: 7391: 7386: 7381: 7380: 7379: 7374: 7369: 7364: 7359: 7349: 7347:Computable set 7344: 7339: 7334: 7329: 7323: 7321: 7315: 7314: 7312: 7311: 7306: 7301: 7296: 7291: 7286: 7281: 7276: 7275: 7274: 7269: 7264: 7254: 7249: 7244: 7242:Satisfiability 7239: 7234: 7229: 7228: 7227: 7217: 7216: 7215: 7205: 7204: 7203: 7198: 7193: 7188: 7183: 7173: 7172: 7171: 7166: 7159:Interpretation 7155: 7153: 7147: 7146: 7144: 7143: 7138: 7133: 7128: 7123: 7113: 7108: 7107: 7106: 7105: 7104: 7094: 7089: 7079: 7074: 7069: 7064: 7059: 7054: 7048: 7046: 7040: 7039: 7036: 7035: 7033: 7032: 7024: 7023: 7022: 7021: 7016: 7015: 7014: 7009: 7004: 6984: 6983: 6982: 6980:minimal axioms 6977: 6966: 6965: 6964: 6953: 6952: 6951: 6946: 6941: 6936: 6931: 6926: 6913: 6911: 6892: 6891: 6889: 6888: 6887: 6886: 6874: 6869: 6868: 6867: 6862: 6857: 6852: 6842: 6837: 6832: 6827: 6826: 6825: 6820: 6810: 6809: 6808: 6803: 6798: 6793: 6783: 6778: 6777: 6776: 6771: 6766: 6756: 6755: 6754: 6749: 6744: 6739: 6734: 6729: 6719: 6714: 6709: 6704: 6703: 6702: 6697: 6692: 6687: 6677: 6672: 6670:Formation rule 6667: 6662: 6661: 6660: 6655: 6645: 6644: 6643: 6633: 6628: 6623: 6618: 6612: 6606: 6589:Formal systems 6585: 6584: 6581: 6580: 6578: 6577: 6572: 6567: 6562: 6557: 6552: 6547: 6542: 6537: 6532: 6531: 6530: 6525: 6514: 6512: 6508: 6507: 6505: 6504: 6503: 6502: 6492: 6487: 6486: 6485: 6478:Large cardinal 6475: 6470: 6465: 6460: 6455: 6441: 6440: 6439: 6434: 6429: 6414: 6412: 6402: 6401: 6399: 6398: 6397: 6396: 6391: 6386: 6376: 6371: 6366: 6361: 6356: 6351: 6346: 6341: 6336: 6331: 6326: 6321: 6315: 6313: 6306: 6305: 6303: 6302: 6301: 6300: 6295: 6290: 6285: 6280: 6275: 6267: 6266: 6265: 6260: 6250: 6245: 6243:Extensionality 6240: 6238:Ordinal number 6235: 6225: 6220: 6219: 6218: 6207: 6201: 6195: 6194: 6191: 6190: 6188: 6187: 6182: 6177: 6172: 6167: 6162: 6157: 6156: 6155: 6145: 6144: 6143: 6130: 6128: 6122: 6121: 6119: 6118: 6117: 6116: 6111: 6106: 6096: 6091: 6086: 6081: 6076: 6071: 6065: 6063: 6057: 6056: 6054: 6053: 6048: 6043: 6038: 6033: 6028: 6023: 6022: 6021: 6011: 6006: 6001: 5996: 5991: 5986: 5980: 5978: 5969: 5963: 5962: 5960: 5959: 5954: 5949: 5944: 5939: 5934: 5922:Cantor's  5920: 5915: 5910: 5900: 5898: 5885: 5884: 5882: 5881: 5876: 5871: 5866: 5861: 5856: 5851: 5846: 5841: 5836: 5831: 5826: 5821: 5820: 5819: 5808: 5806: 5802: 5801: 5794: 5793: 5786: 5779: 5771: 5763: 5762: 5740: 5739: 5736: 5735: 5710: 5698:Reprinted in: 5677: 5671: 5650: 5603:(1): 105–110. 5583: 5516: 5506: 5479: 5412: 5384: 5358: 5343: 5306: 5278: 5254: 5235: 5211: 5186: 5179: 5160: 5159: 5157: 5154: 5153: 5152: 5147: 5142: 5137: 5132: 5127: 5122: 5117: 5110: 5107: 5094: 5083: 5082: 5064: 5060: 5056: 5052: 5028: 5017: 5016: 4997: 4994: 4991: 4988: 4984: 4980: 4976: 4972: 4969: 4966: 4943: 4940: 4937: 4934: 4914: 4911: 4908: 4905: 4902: 4899: 4896: 4893: 4890: 4887: 4883: 4879: 4876: 4873: 4870: 4867: 4864: 4853: 4852: 4841: 4838: 4828: 4825: 4822: 4819: 4816: 4813: 4810: 4807: 4804: 4801: 4798: 4794: 4783: 4780: 4777: 4774: 4771: 4761: 4757: 4753: 4749: 4701: 4689: 4678: 4677: 4676: 4665: 4661: 4658: 4655: 4651: 4647: 4644: 4641: 4637: 4633: 4629: 4626: 4623: 4619: 4615: 4611: 4607: 4604: 4601: 4597: 4574: 4573: 4562: 4558: 4555: 4552: 4548: 4544: 4541: 4538: 4534: 4530: 4526: 4523: 4520: 4516: 4485:Main article: 4482: 4479: 4478: 4477: 4465: 4462: 4459: 4456: 4453: 4435: 4404: 4373: 4300: 4297: 4296: 4295: 4284: 4278: 4273: 4269: 4262: 4258: 4254: 4249: 4243: 4239: 4233: 4227: 4220: 4216: 4211: 4207: 4202: 4196: 4189: 4176: 4165: 4160: 4155: 4148: 4144: 4139: 4135: 4127: 4123: 4118: 4112: 4108: 4102: 4098: 4091: 4087: 4081: 4074: 4070: 4065: 4061: 4056: 4049: 4045: 4038: 4025: 4014: 4009: 4004: 3997: 3993: 3988: 3984: 3976: 3972: 3967: 3964: 3960: 3956: 3951: 3946: 3939: 3935: 3930: 3926: 3921: 3916: 3910: 3877: 3872: 3868: 3862: 3855: 3832: 3827: 3822: 3815: 3811: 3804: 3782: 3777: 3772: 3767: 3761: 3744: 3743: 3736: 3723: 3718: 3713: 3709: 3705: 3699: 3694: 3679: 3678: 3677: 3676: 3662: 3614: 3586:Giuseppe Peano 3573:(−œπ, Ϲ) and 3536:proper subsets 3514: 3513: 3500: 3496: 3492: 3485: 3481: 3476: 3453: 3452: 3441: 3428: 3424: 3420: 3413: 3409: 3404: 3374: 3370: 3366: 3359: 3355: 3350: 3346: 3341: 3309: 3305: 3282: 3261:Main article: 3258: 3255: 3240: 3236: 3195: 3192: 3191: 3190: 3168: 3139: 3121: 3117: 3093: 3057: 3054: 3027: 3023: 2998: 2994: 2989: 2964: 2960: 2955: 2951: 2946: 2942: 2910: 2906: 2901: 2897: 2892: 2868: 2864: 2860: 2855: 2834:fraktur script 2819: 2791: 2787: 2753: 2749: 2726: 2723: 2720: 2716: 2695: 2681: 2680: 2669: 2666: 2663: 2658: 2654: 2650: 2645: 2641: 2637: 2632: 2628: 2605: 2604: 2589:representative 2585: 2554:equinumerosity 2543:Main article: 2540: 2537: 2509: 2483: 2458: 2454: 2450: 2445: 2418: 2393: 2389: 2385: 2380: 2353: 2330: 2327: 2324: 2321: 2318: 2315: 2312: 2309: 2287: 2283: 2279: 2274: 2240: 2212: 2188: 2164: 2140: 2127: 2112: 2097: 2073: 2050: 2046: 2042: 2038: 2034: 2030: 2026: 2004: 2000: 1996: 1992: 1988: 1984: 1980: 1950: 1946: 1942: 1938: 1934: 1930: 1926: 1904: 1900: 1896: 1892: 1888: 1884: 1880: 1858: 1854: 1850: 1846: 1842: 1838: 1834: 1808: 1784: 1760: 1736: 1723: 1708: 1693: 1670: 1665: 1660: 1656: 1652: 1648: 1644: 1634:can challenge 1621: 1597: 1571: 1568: 1560: 1557: 1554: 1551: 1548: 1545: 1542: 1539: 1536: 1514: 1489: 1464: 1442: 1439: 1436: 1433: 1430: 1427: 1424: 1402: 1377: 1352: 1328: 1304: 1280: 1256: 1228: 1204: 1176: 1152: 1125: 1100: 1077: 1074: 1071: 1068: 1065: 1062: 1059: 1035: 1027: 1024: 1021: 1018: 1015: 1012: 1009: 1006: 1003: 1000: 996: 971: 963: 960: 957: 954: 951: 948: 945: 942: 939: 936: 933: 886: 862: 834: 810: 792: 777: 617: 616:Comparing sets 614: 532: 529: 516: 513: 493: 490: 487: 484: 481: 460: 439: 436: 433: 430: 410: 399:absolute value 381: 377: 373: 352: 327: 323: 319: 315: 311: 307: 303: 280: 256: 203: 200: 197: 194: 191: 188: 185: 182: 179: 159: 156: 153: 150: 147: 144: 141: 138: 135: 99: 96: 92: 88: 84: 63: 39: 15: 9: 6: 4: 3: 2: 8205: 8194: 8191: 8189: 8186: 8185: 8183: 8168: 8167:Ernst Zermelo 8165: 8163: 8160: 8158: 8155: 8153: 8152:Willard Quine 8150: 8148: 8145: 8143: 8140: 8138: 8135: 8133: 8130: 8128: 8125: 8123: 8120: 8118: 8115: 8113: 8110: 8109: 8107: 8105: 8104:Set theorists 8101: 8095: 8092: 8090: 8087: 8085: 8082: 8081: 8079: 8073: 8071: 8068: 8067: 8064: 8056: 8053: 8051: 8050:Kripke–Platek 8048: 8044: 8041: 8040: 8039: 8036: 8035: 8034: 8031: 8027: 8024: 8023: 8022: 8021: 8017: 8013: 8010: 8009: 8008: 8005: 8004: 8001: 7998: 7996: 7993: 7991: 7988: 7986: 7983: 7982: 7980: 7976: 7970: 7967: 7965: 7962: 7960: 7957: 7955: 7953: 7948: 7946: 7943: 7941: 7938: 7935: 7931: 7928: 7926: 7923: 7919: 7916: 7914: 7911: 7909: 7906: 7905: 7904: 7901: 7898: 7894: 7891: 7889: 7886: 7884: 7881: 7879: 7876: 7875: 7873: 7870: 7866: 7860: 7857: 7855: 7852: 7850: 7847: 7845: 7842: 7840: 7837: 7835: 7832: 7830: 7827: 7823: 7820: 7818: 7815: 7814: 7813: 7810: 7808: 7805: 7803: 7800: 7798: 7795: 7793: 7790: 7787: 7783: 7780: 7778: 7775: 7773: 7770: 7769: 7767: 7761: 7758: 7757: 7754: 7748: 7745: 7743: 7740: 7738: 7735: 7733: 7730: 7728: 7725: 7723: 7720: 7718: 7715: 7712: 7709: 7707: 7704: 7703: 7701: 7699: 7695: 7687: 7686:specification 7684: 7682: 7679: 7678: 7677: 7674: 7673: 7670: 7667: 7665: 7662: 7660: 7657: 7655: 7652: 7650: 7647: 7645: 7642: 7640: 7637: 7635: 7632: 7630: 7627: 7625: 7622: 7618: 7615: 7613: 7610: 7608: 7605: 7604: 7603: 7600: 7598: 7595: 7594: 7592: 7590: 7586: 7581: 7571: 7568: 7567: 7565: 7561: 7557: 7550: 7545: 7543: 7538: 7536: 7531: 7530: 7527: 7517: 7516: 7511: 7503: 7497: 7494: 7492: 7489: 7487: 7484: 7482: 7479: 7475: 7472: 7471: 7470: 7467: 7465: 7462: 7460: 7457: 7455: 7451: 7448: 7446: 7443: 7441: 7438: 7436: 7433: 7431: 7428: 7427: 7425: 7421: 7415: 7412: 7410: 7407: 7405: 7404:Recursive set 7402: 7400: 7397: 7395: 7392: 7390: 7387: 7385: 7382: 7378: 7375: 7373: 7370: 7368: 7365: 7363: 7360: 7358: 7355: 7354: 7353: 7350: 7348: 7345: 7343: 7340: 7338: 7335: 7333: 7330: 7328: 7325: 7324: 7322: 7320: 7316: 7310: 7307: 7305: 7302: 7300: 7297: 7295: 7292: 7290: 7287: 7285: 7282: 7280: 7277: 7273: 7270: 7268: 7265: 7263: 7260: 7259: 7258: 7255: 7253: 7250: 7248: 7245: 7243: 7240: 7238: 7235: 7233: 7230: 7226: 7223: 7222: 7221: 7218: 7214: 7213:of arithmetic 7211: 7210: 7209: 7206: 7202: 7199: 7197: 7194: 7192: 7189: 7187: 7184: 7182: 7179: 7178: 7177: 7174: 7170: 7167: 7165: 7162: 7161: 7160: 7157: 7156: 7154: 7152: 7148: 7142: 7139: 7137: 7134: 7132: 7129: 7127: 7124: 7121: 7120:from ZFC 7117: 7114: 7112: 7109: 7103: 7100: 7099: 7098: 7095: 7093: 7090: 7088: 7085: 7084: 7083: 7080: 7078: 7075: 7073: 7070: 7068: 7065: 7063: 7060: 7058: 7055: 7053: 7050: 7049: 7047: 7045: 7041: 7031: 7030: 7026: 7025: 7020: 7019:non-Euclidean 7017: 7013: 7010: 7008: 7005: 7003: 7002: 6998: 6997: 6995: 6992: 6991: 6989: 6985: 6981: 6978: 6976: 6973: 6972: 6971: 6967: 6963: 6960: 6959: 6958: 6954: 6950: 6947: 6945: 6942: 6940: 6937: 6935: 6932: 6930: 6927: 6925: 6922: 6921: 6919: 6915: 6914: 6912: 6907: 6901: 6896:Example  6893: 6885: 6880: 6879: 6878: 6875: 6873: 6870: 6866: 6863: 6861: 6858: 6856: 6853: 6851: 6848: 6847: 6846: 6843: 6841: 6838: 6836: 6833: 6831: 6828: 6824: 6821: 6819: 6816: 6815: 6814: 6811: 6807: 6804: 6802: 6799: 6797: 6794: 6792: 6789: 6788: 6787: 6784: 6782: 6779: 6775: 6772: 6770: 6767: 6765: 6762: 6761: 6760: 6757: 6753: 6750: 6748: 6745: 6743: 6740: 6738: 6735: 6733: 6730: 6728: 6725: 6724: 6723: 6720: 6718: 6715: 6713: 6710: 6708: 6705: 6701: 6698: 6696: 6693: 6691: 6688: 6686: 6683: 6682: 6681: 6678: 6676: 6673: 6671: 6668: 6666: 6663: 6659: 6656: 6654: 6653:by definition 6651: 6650: 6649: 6646: 6642: 6639: 6638: 6637: 6634: 6632: 6629: 6627: 6624: 6622: 6619: 6617: 6614: 6613: 6610: 6607: 6605: 6601: 6596: 6590: 6586: 6576: 6573: 6571: 6568: 6566: 6563: 6561: 6558: 6556: 6553: 6551: 6548: 6546: 6543: 6541: 6540:Kripke–Platek 6538: 6536: 6533: 6529: 6526: 6524: 6521: 6520: 6519: 6516: 6515: 6513: 6509: 6501: 6498: 6497: 6496: 6493: 6491: 6488: 6484: 6481: 6480: 6479: 6476: 6474: 6471: 6469: 6466: 6464: 6461: 6459: 6456: 6453: 6449: 6445: 6442: 6438: 6435: 6433: 6430: 6428: 6425: 6424: 6423: 6419: 6416: 6415: 6413: 6411: 6407: 6403: 6395: 6392: 6390: 6387: 6385: 6384:constructible 6382: 6381: 6380: 6377: 6375: 6372: 6370: 6367: 6365: 6362: 6360: 6357: 6355: 6352: 6350: 6347: 6345: 6342: 6340: 6337: 6335: 6332: 6330: 6327: 6325: 6322: 6320: 6317: 6316: 6314: 6312: 6307: 6299: 6296: 6294: 6291: 6289: 6286: 6284: 6281: 6279: 6276: 6274: 6271: 6270: 6268: 6264: 6261: 6259: 6256: 6255: 6254: 6251: 6249: 6246: 6244: 6241: 6239: 6236: 6234: 6230: 6226: 6224: 6221: 6217: 6214: 6213: 6212: 6209: 6208: 6205: 6202: 6200: 6196: 6186: 6183: 6181: 6178: 6176: 6173: 6171: 6168: 6166: 6163: 6161: 6158: 6154: 6151: 6150: 6149: 6146: 6142: 6137: 6136: 6135: 6132: 6131: 6129: 6127: 6123: 6115: 6112: 6110: 6107: 6105: 6102: 6101: 6100: 6097: 6095: 6092: 6090: 6087: 6085: 6082: 6080: 6077: 6075: 6072: 6070: 6067: 6066: 6064: 6062: 6061:Propositional 6058: 6052: 6049: 6047: 6044: 6042: 6039: 6037: 6034: 6032: 6029: 6027: 6024: 6020: 6017: 6016: 6015: 6012: 6010: 6007: 6005: 6002: 6000: 5997: 5995: 5992: 5990: 5989:Logical truth 5987: 5985: 5982: 5981: 5979: 5977: 5973: 5970: 5968: 5964: 5958: 5955: 5953: 5950: 5948: 5945: 5943: 5940: 5938: 5935: 5933: 5929: 5925: 5921: 5919: 5916: 5914: 5911: 5909: 5905: 5902: 5901: 5899: 5897: 5891: 5886: 5880: 5877: 5875: 5872: 5870: 5867: 5865: 5862: 5860: 5857: 5855: 5852: 5850: 5847: 5845: 5842: 5840: 5837: 5835: 5832: 5830: 5827: 5825: 5822: 5818: 5815: 5814: 5813: 5810: 5809: 5807: 5803: 5799: 5792: 5787: 5785: 5780: 5778: 5773: 5772: 5769: 5759: 5755: 5751: 5745: 5741: 5732: 5731:0-85312-563-5 5728: 5724: 5723:0-85312-612-7 5720: 5714: 5705: 5704: 5694: 5690: 5689: 5681: 5674: 5672:0-09-944068-7 5668: 5664: 5660: 5654: 5646: 5642: 5637: 5632: 5628: 5624: 5619: 5614: 5610: 5606: 5602: 5598: 5594: 5587: 5579: 5575: 5570: 5565: 5561: 5557: 5552: 5547: 5543: 5539: 5535: 5531: 5527: 5520: 5514: 5509: 5507:3-540-42224-2 5503: 5499: 5498: 5493: 5489: 5483: 5476: 5472: 5468: 5464: 5460: 5456: 5452: 5448: 5447: 5442: 5438: 5434: 5433:David Hilbert 5430: 5426: 5422: 5416: 5401: 5397: 5391: 5389: 5380: 5376: 5369: 5362: 5354: 5347: 5328: 5324: 5317: 5310: 5303: 5299: 5295: 5291: 5288: 5282: 5268: 5267:Math Timeline 5264: 5258: 5251: 5247: 5246: 5239: 5225: 5224:brilliant.org 5221: 5215: 5206: 5205: 5200: 5197: 5190: 5182: 5176: 5172: 5165: 5161: 5151: 5148: 5146: 5143: 5141: 5138: 5136: 5135:Countable set 5133: 5131: 5128: 5126: 5123: 5121: 5118: 5116: 5113: 5112: 5106: 5092: 5062: 5054: 5042: 5041: 5040: 5026: 4992: 4989: 4978: 4967: 4957: 4956: 4955: 4941: 4938: 4932: 4909: 4906: 4903: 4900: 4897: 4894: 4891: 4874: 4871: 4868: 4865: 4826: 4820: 4814: 4808: 4805: 4802: 4781: 4778: 4772: 4769: 4759: 4751: 4739: 4738: 4737: 4699: 4687: 4683: 4663: 4659: 4656: 4653: 4649: 4645: 4642: 4639: 4635: 4631: 4627: 4624: 4621: 4617: 4613: 4609: 4605: 4602: 4599: 4595: 4587: 4586: 4585: 4583: 4582:intersections 4579: 4560: 4556: 4553: 4550: 4546: 4542: 4539: 4536: 4532: 4528: 4524: 4521: 4518: 4514: 4506: 4505: 4504: 4502: 4501:disjoint sets 4498: 4494: 4488: 4460: 4457: 4454: 4443: 4439: 4436: 4433: 4429: 4425: 4421: 4417: 4413: 4409: 4405: 4402: 4398: 4394: 4390: 4386: 4382: 4378: 4374: 4371: 4367: 4363: 4359: 4355: 4352:, oranges), ( 4351: 4347: 4344:| because { ( 4343: 4339: 4335: 4331: 4327: 4323: 4319: 4315: 4311: 4307: 4303: 4302: 4282: 4271: 4267: 4260: 4252: 4241: 4237: 4225: 4218: 4209: 4205: 4200: 4177: 4163: 4153: 4146: 4137: 4133: 4125: 4116: 4110: 4100: 4096: 4089: 4079: 4072: 4063: 4059: 4054: 4047: 4026: 4012: 4002: 3995: 3986: 3982: 3974: 3965: 3962: 3958: 3954: 3949: 3944: 3937: 3928: 3924: 3919: 3914: 3898: 3897: 3896: 3894: 3870: 3866: 3830: 3820: 3813: 3780: 3770: 3765: 3749: 3741: 3737: 3716: 3711: 3707: 3703: 3692: 3684: 3683: 3682: 3675: 3671: 3667: 3663: 3660: 3656: 3652: 3648: 3644: 3640: 3639: 3638: 3637: 3636: 3634: 3630: 3601: 3599: 3595: 3591: 3587: 3582: 3580: 3576: 3572: 3568: 3564: 3559: 3557: 3553: 3549: 3545: 3541: 3537: 3533: 3529: 3524: 3522: 3519: 3498: 3490: 3483: 3474: 3466: 3465: 3464: 3462: 3458: 3450: 3446: 3442: 3426: 3418: 3411: 3402: 3394: 3393: 3392: 3391:) satisfies: 3390: 3372: 3368: 3364: 3357: 3348: 3344: 3329: 3325: 3307: 3270: 3264: 3254: 3238: 3225: 3221: 3217: 3213: 3212:Gottlob Frege 3209: 3205: 3204:infinite sets 3201: 3194:Infinite sets 3188: 3184: 3156: 3152: 3148: 3144: 3140: 3137: 3119: 3106: 3102: 3098: 3094: 3091: 3087: 3083: 3079: 3075: 3071: 3070: 3069: 3067: 3063: 3053: 3051: 3047: 3043: 3025: 2996: 2987: 2962: 2953: 2949: 2944: 2931: 2926: 2908: 2899: 2895: 2866: 2858: 2843: 2839: 2835: 2807: 2789: 2776: 2772: 2767: 2751: 2724: 2721: 2718: 2693: 2686: 2667: 2664: 2661: 2656: 2648: 2643: 2635: 2630: 2618: 2617: 2616: 2614: 2613:infinite sets 2610: 2607:Assuming the 2602: 2598: 2594: 2590: 2586: 2583: 2579: 2578: 2577: 2575: 2571: 2567: 2563: 2559: 2555: 2550: 2546: 2536: 2534: 2530: 2526: 2325: 2319: 2313: 2307: 2261: 2257: 2226: 2210: 2186: 2162: 2138: 2124: 2118: 2111: 2095: 2071: 2044: 2036: 2028: 1998: 1990: 1982: 1969: 1965: 1944: 1936: 1928: 1898: 1890: 1882: 1852: 1844: 1836: 1822: 1806: 1782: 1758: 1734: 1720: 1714: 1707: 1691: 1654: 1646: 1619: 1595: 1585: 1566: 1558: 1552: 1549: 1546: 1540: 1534: 1527:, defined by 1512: 1462: 1440: 1437: 1434: 1428: 1422: 1415:, defined by 1400: 1350: 1326: 1302: 1278: 1254: 1244: 1226: 1202: 1192: 1174: 1150: 1139: 1123: 1075: 1072: 1069: 1063: 1057: 1049: 1025: 1022: 1019: 1016: 1013: 1010: 1007: 1004: 998: 985: 961: 958: 955: 952: 949: 946: 943: 940: 934: 931: 922: 920: 919: 914: 910: 906: 902: 899:that is both 884: 860: 850: 847:, that is, a 832: 808: 798: 789: 783: 776: 769: 765: 761: 757: 752: 747: 743: 739: 735: 730: 725: 721: 717: 713: 709: 705: 701: 697: 693: 689: 685: 681: 677: 673: 669: 665: 661: 658: 654: 650: 643: 639: 635: 631: 627: 622: 613: 611: 607: 603: 599: 595: 583: 581: 577: 573: 569: 565: 561: 557: 556: 549: 547: 528: 514: 488: 482: 479: 458: 434: 428: 408: 400: 396: 375: 350: 342: 321: 313: 305: 278: 254: 243: 241: 237: 233: 229: 225: 221: 220:infinite sets 217: 198: 195: 192: 189: 186: 180: 177: 154: 151: 148: 145: 142: 136: 133: 125: 121: 117: 97: 94: 86: 61: 53: 37: 28: 22: 8117:Georg Cantor 8112:Paul Bernays 8043:Morse–Kelley 8018: 7951: 7950:Subset  7897:hereditarily 7859:Venn diagram 7817:ordered pair 7776: 7732:Intersection 7676:Axiom schema 7506: 7304:Ultraproduct 7151:Model theory 7116:Independence 7052:Formal proof 7044:Proof theory 7027: 7000: 6957:real numbers 6929:second-order 6840:Substitution 6717:Metalanguage 6658:conservative 6631:Axiom schema 6575:Constructive 6545:Morse–Kelley 6511:Set theories 6490:Aleph number 6483:inaccessible 6409: 6389:Grothendieck 6273:intersection 6160:Higher-order 6148:Second-order 6094:Truth tables 6051:Venn diagram 5834:Formal proof 5823: 5744: 5713: 5702: 5692: 5686: 5680: 5662: 5653: 5600: 5596: 5586: 5533: 5529: 5519: 5496: 5482: 5450: 5444: 5415: 5404:. Retrieved 5402:. 2019-12-05 5399: 5378: 5374: 5361: 5352: 5346: 5334:. Retrieved 5327:the original 5322: 5309: 5297: 5281: 5270:. Retrieved 5266: 5257: 5243: 5238: 5227:. Retrieved 5223: 5214: 5202: 5189: 5170: 5164: 5115:Aleph number 5084: 5018: 4925:, therefore 4854: 4691: 4575: 4496: 4492: 4490: 4427: 4423: 4419: 4415: 4411: 4407: 4400: 4396: 4392: 4388: 4387:such that | 4384: 4380: 4376: 4369: 4365: 4361: 4357: 4353: 4349: 4348:, apples), ( 4345: 4341: 4337: 4333: 4329: 4325: 4321: 4317: 4313: 4309: 4305: 3745: 3680: 3673: 3669: 3665: 3658: 3654: 3650: 3645:, i.e., the 3642: 3602: 3598:such a proof 3583: 3574: 3569:between the 3560: 3555: 3551: 3547: 3543: 3525: 3515: 3454: 3327: 3323: 3266: 3208:Georg Cantor 3197: 3182: 3154: 3150: 3146: 3142: 3104: 3100: 3096: 3085: 3081: 3073: 3059: 2927: 2806:real numbers 2768: 2682: 2615:are denoted 2606: 2581: 2573: 2569: 2551: 2548: 2525:real numbers 2227: 2129: 2122: 2116: 1823: 1725: 1718: 1712: 1242: 1190: 1140: 984:even numbers 923: 918:equinumerous 916: 912: 908: 794: 787: 781: 773: 767: 763: 759: 755: 750: 745: 741: 737: 733: 728: 723: 719: 715: 711: 703: 699: 695: 691: 687: 683: 679: 675: 671: 667: 663: 659: 652: 641: 637: 634:even numbers 629: 625: 594:Georg Cantor 584: 575: 571: 567: 563: 553: 550: 536:as early as 534: 395:vertical bar 340: 244: 239: 119: 113: 8142:Thomas Jech 7985:Alternative 7964:Uncountable 7918:Ultrafilter 7777:Cardinality 7681:replacement 7629:Determinacy 7414:Type theory 7362:undecidable 7294:Truth value 7181:equivalence 6860:non-logical 6473:Enumeration 6463:Isomorphism 6410:cardinality 6394:Von Neumann 6359:Ultrafilter 6324:Uncountable 6258:equivalence 6175:Quantifiers 6165:Fixed-point 6134:First-order 6014:Consistency 5999:Proposition 5976:Traditional 5947:Lindström's 5937:Compactness 5879:Type theory 5824:Cardinality 5425:Felix Klein 5120:Beth number 3550:, although 3200:finite sets 3187:uncountable 3064:holds, the 3042:independent 2773:is denoted 913:equipollent 682:), the set 636:. Although 628:to the set 590: 1880 546:mathematics 120:cardinality 116:mathematics 8182:Categories 8137:Kurt Gödel 8122:Paul Cohen 7959:Transitive 7727:Identities 7711:Complement 7698:Operations 7659:Regularity 7597:Adjunction 7556:Set theory 7225:elementary 6918:arithmetic 6786:Quantifier 6764:functional 6636:Expression 6354:Transitive 6298:identities 6283:complement 6216:hereditary 6199:Set theory 5659:Penrose, R 5406:2020-08-23 5272:2018-04-26 5229:2020-08-23 5156:References 5145:Ordinality 4422:|, then | 3653:, written 3577:(see also 3090:finite set 2932:says that 2775:aleph-null 2300:, because 2062:for every 909:equipotent 905:surjective 598:set theory 232:injections 228:bijections 224:arithmetic 8070:Paradoxes 7990:Axiomatic 7969:Universal 7945:Singleton 7940:Recursive 7883:Countable 7878:Amorphous 7737:Power set 7654:Power set 7612:dependent 7607:countable 7496:Supertask 7399:Recursion 7357:decidable 7191:saturated 7169:of models 7092:deductive 7087:axiomatic 7007:Hilbert's 6994:Euclidean 6975:canonical 6898:axiomatic 6830:Signature 6759:Predicate 6648:Extension 6570:Ackermann 6495:Operation 6374:Universal 6364:Recursive 6339:Singleton 6334:Inhabited 6319:Countable 6309:Types of 6293:power set 6263:partition 6180:Predicate 6126:Predicate 6041:Syllogism 6031:Soundness 6004:Inference 5994:Tautology 5896:paradoxes 5475:121598654 5467:0025-5831 5204:MathWorld 4996:→ 4971:↦ 4936:∅ 4933:⋂ 4907:∈ 4895:∈ 4889:∀ 4882:⟺ 4872:⋂ 4869:∈ 4815:α 4812:→ 4797:∃ 4782:∈ 4779:α 4773:⋂ 4770:∩ 4625:∩ 4603:∪ 4522:∪ 4257:ℵ 4253:× 4215:ℵ 4143:ℵ 4122:ℵ 4117:× 4107:ℵ 4086:ℵ 4069:ℵ 4044:ℵ 3992:ℵ 3971:ℵ 3966:× 3934:ℵ 3810:ℵ 3708:ℶ 3647:power set 3594:hypercube 3495:ℵ 3480:ℵ 3423:ℵ 3408:ℵ 3369:ℶ 3354:ℵ 3304:ℵ 3235:ℵ 3149:| > | 3116:ℵ 3084:| < | 3022:ℵ 2993:ℵ 2959:ℵ 2941:ℵ 2905:ℵ 2863:ℵ 2786:ℵ 2752:α 2748:ℵ 2719:α 2715:ℵ 2694:α 2683:For each 2665:… 2653:ℵ 2640:ℵ 2627:ℵ 2568:of a set 2260:power set 2037:≤ 1991:≤ 1891:≤ 1845:≤ 1553:− 901:injective 797:bijection 657:power set 602:bijection 512:# 483:⁡ 393:, with a 8074:Problems 7978:Theories 7954:Superset 7930:Infinite 7759:Concepts 7639:Infinity 7563:Overview 7481:Logicism 7474:timeline 7450:Concrete 7309:Validity 7279:T-schema 7272:Kripke's 7267:Tarski's 7262:semantic 7252:Strength 7201:submodel 7196:spectrum 7164:function 7012:Tarski's 7001:Elements 6988:geometry 6944:Robinson 6865:variable 6850:function 6823:spectrum 6813:Sentence 6769:variable 6712:Language 6665:Relation 6626:Automata 6616:Alphabet 6600:language 6454:-jection 6432:codomain 6418:Function 6379:Universe 6349:Infinite 6253:Relation 6036:Validity 6026:Argument 5924:theorem, 5758:geometry 5748:Such as 5695:: 81–125 5661:(2005), 5645:16591132 5578:16578557 5490:(2002), 5439:(eds.), 5423:(1915), 5381:: 75–78. 5290:Archived 5140:Counting 5109:See also 4414:| and | 3740:Beth two 3664:the set 3571:interval 3389:Beth one 3141:Any set 3095:Any set 3072:Any set 849:function 714:, hence 555:Elements 216:elements 30:The set 8012:General 8007:Zermelo 7913:subbase 7895: ( 7834:Forcing 7812:Element 7784: ( 7762:Methods 7649:Pairing 7423:Related 7220:Diagram 7118: ( 7097:Hilbert 7082:Systems 7077:Theorem 6955:of the 6900:systems 6680:Formula 6675:Grammar 6591: ( 6535:General 6248:Forcing 6233:Element 6153:Monadic 5928:paradox 5869:Theorem 5805:General 5605:Bibcode 5538:Bibcode 5336:Nov 15, 4503:, then 3633:theorem 3532:segment 3181:> | 3080:, or | 3060:If the 3052:below. 2979:, i.e. 2844:, that 2685:ordinal 2560:on the 2523:of all 2521:⁠ 2499:⁠ 2495:⁠ 2473:⁠ 2469:⁠ 2434:⁠ 2430:⁠ 2408:⁠ 2404:⁠ 2369:⁠ 2365:⁠ 2343:⁠ 2298:⁠ 2263:⁠ 2254:of all 2252:⁠ 2230:⁠ 2223:⁠ 2203:⁠ 2199:⁠ 2179:⁠ 2175:⁠ 2155:⁠ 2151:⁠ 2131:⁠ 2108:⁠ 2088:⁠ 2084:⁠ 2064:⁠ 1966:). The 1916:, then 1819:⁠ 1799:⁠ 1795:⁠ 1775:⁠ 1771:⁠ 1751:⁠ 1747:⁠ 1727:⁠ 1704:⁠ 1684:⁠ 1632:⁠ 1612:⁠ 1608:⁠ 1588:⁠ 1525:⁠ 1505:⁠ 1501:⁠ 1479:⁠ 1475:⁠ 1455:⁠ 1413:⁠ 1393:⁠ 1389:⁠ 1367:⁠ 1363:⁠ 1343:⁠ 1339:⁠ 1319:⁠ 1315:⁠ 1295:⁠ 1291:⁠ 1271:⁠ 1267:⁠ 1247:⁠ 1241:, then 1239:⁠ 1219:⁠ 1215:⁠ 1195:⁠ 1187:⁠ 1167:⁠ 1163:⁠ 1143:⁠ 1136:⁠ 1116:⁠ 1112:⁠ 1090:⁠ 897:⁠ 877:⁠ 873:⁠ 853:⁠ 845:⁠ 825:⁠ 821:⁠ 801:⁠ 531:History 291:⁠ 271:⁠ 267:⁠ 247:⁠ 50:of all 7903:Filter 7893:Finite 7829:Family 7772:Almost 7617:global 7602:Choice 7589:Axioms 7186:finite 6949:Skolem 6902:  6877:Theory 6845:Symbol 6835:String 6818:atomic 6695:ground 6690:closed 6685:atomic 6641:ground 6604:syntax 6500:binary 6427:domain 6344:Finite 6109:finite 5967:Logics 5926:  5874:Theory 5750:length 5729:  5721:  5669:  5643:  5636:300611 5633:  5625:  5576:  5569:221287 5566:  5558:  5504:  5473:  5465:  5250:Quanta 5177:  4578:unions 4426:| = | 4418:| ≀ | 4410:| ≀ | 4395:| and 4391:| = | 4379:| ≀ | 4340:| = | 4332:, and 4320:} and 3661:) or 2 3103:| = | 2126:| 1722:| 1582:(see: 791:| 7995:Naive 7925:Fuzzy 7888:Empty 7871:types 7822:tuple 7792:Class 7786:large 7747:Union 7664:Union 7176:Model 6924:Peano 6781:Proof 6621:Arity 6550:Naive 6437:image 6369:Fuzzy 6329:Empty 6278:union 6223:Class 5864:Model 5854:Lemma 5812:Axiom 5627:72252 5623:JSTOR 5560:71858 5556:JSTOR 5471:S2CID 5371:(PDF) 5330:(PDF) 5319:(PDF) 4692:Here 4580:and 4406:If | 4375:If | 4372:is 3. 3738:(see 3443:(see 3387:(see 2562:class 1797:into 1477:from 1365:from 1189:, if 915:, or 851:from 708:range 670:from 504:, or 7908:base 7299:Type 7102:list 6906:list 6883:list 6872:Term 6806:rank 6700:open 6594:list 6406:Maps 6311:sets 6170:Free 6140:list 5890:list 5817:list 5754:area 5752:and 5727:ISBN 5719:ISBN 5667:ISBN 5641:PMID 5574:PMID 5502:ISBN 5463:ISSN 5338:2019 5175:ISBN 4499:are 4495:and 4368:and 4360:and 3843:and 3746:The 3717:> 3631:and 3538:and 3455:The 3419:> 3157:| = 3138:set. 3107:| = 2928:The 2859:> 2662:< 2649:< 2636:< 2086:and 1870:and 1610:nor 1317:and 1243:each 1191:some 1165:and 903:and 751:blue 574:and 566:and 480:card 269:and 240:size 230:and 170:and 124:sets 7869:Set 6986:of 6968:of 6916:of 6448:Sur 6422:Map 6229:Ur- 6211:Set 5756:in 5631:PMC 5613:doi 5564:PMC 5546:doi 5455:doi 5068:Ord 5001:Ord 4787:Ord 4765:Ord 4722:Ord 4684:or 4682:NBG 4491:If 4308:= { 4304:If 3672:to 3649:of 3581:). 3518:ZFC 3447:or 3253:). 3046:ZFC 3044:of 2599:in 2531:or 2432:to 2367:to 2201:to 2016:or 1824:If 1503:to 1391:to 1269:to 1217:to 1114:to 1046:of 1030:... 966:... 921:. 875:to 823:to 729:red 710:of 686:= { 674:to 632:of 592:by 540:000 114:In 8184:: 7372:NP 6996:: 6990:: 6920:: 6597:), 6452:Bi 6444:In 5693:91 5691:, 5639:. 5629:. 5621:. 5611:. 5601:51 5599:. 5595:. 5572:. 5562:. 5554:. 5544:. 5534:50 5532:. 5528:. 5511:- 5469:, 5461:, 5451:76 5449:, 5443:, 5435:; 5431:; 5427:; 5398:. 5387:^ 5377:. 5373:. 5321:. 5300:. 5296:, 5265:. 5248:, 5222:. 5201:. 4760::= 4686:MK 4399:⊆ 4328:, 4316:, 4312:, 3895:: 3742:). 3600:. 3451:). 3214:, 3210:, 2766:. 2706:, 2587:A 2535:. 2225:. 2110:. 1821:. 1706:. 911:, 770:). 748:, 744:)\ 732:: 726:; 694:: 587:c. 558:, 538:40 527:. 472:, 450:, 118:, 7952:· 7936:) 7932:( 7899:) 7788:) 7548:e 7541:t 7534:v 7452:/ 7367:P 7122:) 6908:) 6904:( 6801:∀ 6796:! 6791:∃ 6752:= 6747:↔ 6742:→ 6737:∧ 6732:√ 6727:ÂŹ 6450:/ 6446:/ 6420:/ 6231:) 6227:( 6114:∞ 6104:3 5892:) 5790:e 5783:t 5776:v 5647:. 5615:: 5607:: 5580:. 5548:: 5540:: 5457:: 5409:. 5379:1 5355:. 5340:. 5304:. 5275:. 5232:. 5207:. 5183:. 5093:V 5063:= 5059:| 5055:P 5051:| 5027:P 5015:. 4993:V 4990:: 4987:) 4983:| 4979:x 4975:| 4968:x 4965:( 4942:V 4939:= 4913:) 4910:q 4904:x 4901:: 4898:Q 4892:q 4886:( 4878:) 4875:Q 4866:x 4863:( 4840:} 4837:) 4827:f 4824:( 4821:: 4818:) 4809:A 4806:: 4803:f 4800:( 4793:| 4776:{ 4756:| 4752:A 4748:| 4700:V 4688:) 4664:. 4660:| 4657:D 4654:| 4650:+ 4646:| 4643:C 4640:| 4636:= 4632:| 4628:D 4622:C 4618:| 4614:+ 4610:| 4606:D 4600:C 4596:| 4561:. 4557:| 4554:B 4551:| 4547:+ 4543:| 4540:A 4537:| 4533:= 4529:| 4525:B 4519:A 4515:| 4497:B 4493:A 4476:. 4464:] 4461:1 4458:, 4455:0 4452:[ 4434:. 4428:Y 4424:X 4420:X 4416:Y 4412:Y 4408:X 4403:. 4401:Y 4397:Z 4393:Z 4389:X 4385:Z 4381:Y 4377:X 4370:Y 4366:X 4362:Y 4358:X 4354:c 4350:b 4346:a 4342:Y 4338:X 4334:c 4330:b 4326:a 4322:Y 4318:c 4314:b 4310:a 4306:X 4283:. 4277:c 4272:2 4268:= 4261:0 4248:c 4242:2 4238:= 4232:c 4226:) 4219:0 4210:2 4206:( 4201:= 4195:c 4188:c 4164:, 4159:c 4154:= 4147:0 4138:2 4134:= 4126:0 4111:0 4101:2 4097:= 4090:0 4080:) 4073:0 4064:2 4060:( 4055:= 4048:0 4037:c 4013:, 4008:c 4003:= 3996:0 3987:2 3983:= 3975:0 3963:2 3959:2 3955:= 3950:2 3945:) 3938:0 3929:2 3925:( 3920:= 3915:2 3909:c 3876:c 3871:2 3867:= 3861:c 3854:c 3831:, 3826:c 3821:= 3814:0 3803:c 3781:, 3776:c 3771:= 3766:2 3760:c 3722:c 3712:2 3704:= 3698:c 3693:2 3674:R 3670:R 3666:R 3659:R 3657:( 3655:P 3651:R 3643:R 3613:c 3575:R 3556:S 3552:S 3548:S 3544:S 3499:1 3491:= 3484:0 3475:2 3427:0 3412:0 3403:2 3373:1 3365:= 3358:0 3349:2 3345:= 3340:c 3328:N 3324:R 3308:0 3281:c 3271:( 3239:0 3189:. 3183:N 3167:c 3155:R 3151:N 3147:X 3143:X 3120:0 3105:N 3101:X 3097:X 3092:. 3086:N 3082:X 3074:X 3026:0 2997:0 2988:2 2963:0 2954:2 2950:= 2945:1 2909:0 2900:2 2896:= 2891:c 2867:0 2854:c 2818:c 2790:0 2777:( 2725:1 2722:+ 2668:. 2657:2 2644:1 2631:0 2603:. 2582:A 2574:A 2570:A 2508:R 2482:N 2457:) 2453:N 2449:( 2444:P 2417:N 2392:) 2388:N 2384:( 2379:P 2352:N 2329:} 2326:n 2323:{ 2320:= 2317:) 2314:n 2311:( 2308:g 2286:) 2282:N 2278:( 2273:P 2239:N 2211:B 2187:A 2163:B 2139:A 2123:B 2117:A 2096:B 2072:A 2049:| 2045:A 2041:| 2033:| 2029:B 2025:| 2003:| 1999:B 1995:| 1987:| 1983:A 1979:| 1949:| 1945:B 1941:| 1937:= 1933:| 1929:A 1925:| 1903:| 1899:A 1895:| 1887:| 1883:B 1879:| 1857:| 1853:B 1849:| 1841:| 1837:A 1833:| 1807:B 1783:A 1759:B 1735:A 1719:B 1713:A 1692:f 1669:| 1664:N 1659:| 1655:= 1651:| 1647:E 1643:| 1620:h 1596:g 1570:) 1567:2 1559:n 1556:( 1550:n 1547:= 1544:) 1541:n 1538:( 1535:h 1513:E 1488:N 1463:h 1441:n 1438:4 1435:= 1432:) 1429:n 1426:( 1423:g 1401:E 1376:N 1351:g 1327:B 1303:A 1279:B 1255:A 1227:B 1203:A 1175:B 1151:A 1124:E 1099:N 1076:n 1073:2 1070:= 1067:) 1064:n 1061:( 1058:f 1034:} 1026:, 1023:3 1020:, 1017:2 1014:, 1011:1 1008:, 1005:0 1002:{ 999:= 995:N 970:} 962:, 959:6 956:, 953:4 950:, 947:2 944:, 941:0 938:{ 935:= 932:E 885:B 861:A 833:B 809:A 788:B 782:A 768:n 766:( 764:f 762:\ 760:T 758:∈ 756:n 754:: 746:T 742:n 740:( 738:f 736:∈ 734:n 724:T 720:f 716:f 712:f 704:n 702:( 700:f 698:∉ 696:n 692:N 690:∈ 688:n 684:T 680:N 678:( 676:P 672:N 668:f 664:N 662:( 660:P 653:N 642:N 638:E 630:E 626:N 576:b 572:a 568:b 564:a 515:A 492:) 489:A 486:( 459:A 438:) 435:A 432:( 429:n 409:A 380:| 376:A 372:| 351:A 326:| 322:B 318:| 314:= 310:| 306:A 302:| 279:B 255:A 202:} 199:6 196:, 193:4 190:, 187:2 184:{ 181:= 178:B 158:} 155:3 152:, 149:2 146:, 143:1 140:{ 137:= 134:A 110:. 98:5 95:= 91:| 87:S 83:| 62:S 38:S 23:.

Index

Cardinality (disambiguation)

Platonic solids
mathematics
sets
elements
infinite sets
arithmetic
bijections
injections
cardinal numbers
vertical bar
absolute value
mathematics
Elements
commensurability
irrational numbers
Georg Cantor
set theory
bijection
Cantor's diagonal argument
uncountable sets

even numbers

power set
range
bijection
function
injective

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