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Compact space

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5496: 5279: 5517: 5485: 644:, under appropriate conditions followed from the version of compactness that was formulated in terms of the existence of finite subcovers. It was this notion of compactness that became the dominant one, because it was not only a stronger property, but it could be formulated in a more general setting with a minimum of additional technical machinery, as it relied only on the structure of the open sets in a space. 5554: 5527: 5507: 486:: the sequence was placed into an interval that was then divided into two equal parts, and a part containing infinitely many terms of the sequence was selected. The process could then be repeated by dividing the resulting smaller interval into smaller and smaller parts – until it closes down on the desired limit point. The full significance of 38: 3173:
to of mapping each infinity to its corresponding unit and every real number to its sign multiplied by the unique number in the positive part of interval that results in its absolute value when divided by one minus itself, and since homeomorphisms preserve covers, the Heine-Borel property can be
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are compact since for any infinite number of points sampled from a disk, some subset of those points must get arbitrarily close either to a point within the disc, or to a point on the boundary. However, an open disk is not compact, because a sequence of points can tend to the boundary – without
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holds for such spaces: a continuous real-valued function on a nonempty compact space is bounded above and attains its supremum. (Slightly more generally, this is true for an upper semicontinuous function.) As a sort of converse to the above statements, the pre-image of a compact space under a
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sequence of functions from a suitable family of functions. The uniform limit of this sequence then played precisely the same role as Bolzano's "limit point". Towards the beginning of the twentieth century, results similar to that of Arzelà and Ascoli began to accumulate in the area of
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if, for any positive epsilon, there exists a compact subset containing all but at most epsilon of the mass of each of the measures. Helly's theorem then asserts that a collection of probability measures is relatively compact for the vague topology if and only if it is
355:, those same sets of points would not accumulate to any point of it, so the open unit interval is not compact. Although subsets (subspaces) of Euclidean space can be compact, the entire space itself is not compact, since it is not bounded. For example, considering 898:
of each point of the space – and to extend it to information that holds globally throughout the space. An example of this phenomenon is Dirichlet's theorem, to which it was originally applied by Heine, that a continuous function on a compact interval is
581:. In the course of the proof, he made use of a lemma that from any countable cover of the interval by smaller open intervals, it was possible to select a finite number of these that also covered it. The significance of this lemma was recognized by 815:
getting arbitrarily close to any point in the interior. Likewise, spheres are compact, but a sphere missing a point is not since a sequence of points can still tend to the missing point, thereby not getting arbitrarily close to any point
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is a metric space, the conditions in the next subsection also apply to all of its subsets. Of all of the equivalent conditions, it is in practice easiest to verify that a subset is closed and bounded, for example, for a closed
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states that a subset of Euclidean space is compact in this sequential sense if and only if it is closed and bounded. Thus, if one chooses an infinite number of points in the closed
478:) had been aware that any bounded sequence of points (in the line or plane, for instance) has a subsequence that must eventually get arbitrarily close to some other point, called a 3052: 419:. In general topological spaces, however, these notions of compactness are not necessarily equivalent. The most useful notion — and the standard definition of the unqualified term 1275: 3376:
A subset of the Banach space of real-valued continuous functions on a compact Hausdorff space is relatively compact if and only if it is equicontinuous and pointwise bounded (
2776: 382: 1462: 4115: 4061: 4034: 4002: 3970: 3679: 3628: 3606: 3340: 3245: 3152: 3106: 3081: 2837: 2741: 1838:– these three conditions are equivalent for metric spaces. The converse is not true; e.g., a countable discrete space satisfies these three conditions, but is not compact. 156: 127: 5062: 3656: 3284: 612:
about a set (such as the continuity of a function) to global information about the set (such as the uniform continuity of a function). This sentiment was expressed by
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exemplify applications of this notion of compactness to classical analysis. Following its initial introduction, various equivalent notions of compactness, including
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Rein analytischer Beweis des Lehrsatzes, dass zwischen je zwey Werthen, die ein entgegengesetzes Resultat gewähren, wenigstens eine reele Wurzel der Gleichung liege
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rather than just numbers or geometrical points. The idea of regarding functions as themselves points of a generalized space dates back to the investigations of
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get arbitrarily close to 0, while the even-numbered ones get arbitrarily close to 1. The given example sequence shows the importance of including the
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is compact; a finite subcover can be obtained by selecting, for each point, an open set containing it. A nontrivial example of a compact space is the (closed)
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Arkhangel'skii, A.V.; Fedorchuk, V.V. (1990). "The basic concepts and constructions of general topology". In Arkhangel'skii, A.V.; Pontrjagin, L.S. (eds.).
2214:, this is equivalent to every maximal ideal being the kernel of an evaluation homomorphism. There are pseudocompact spaces that are not compact, though. 470:
In the 19th century, several disparate mathematical properties were understood that would later be seen as consequences of compactness. On the one hand,
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Purely analytic proof of the theorem that between any two values which give results of opposite sign, there lies at least one real root of the equation
5588: 104:(0,1) would not be compact because it excludes the limiting values of 0 and 1, whereas the closed interval would be compact. Similarly, the space of 2784:. Using the one-point compactification, one can also easily construct compact spaces which are not Hausdorff, by starting with a non-Hausdorff space. 819:
the space. Lines and planes are not compact, since one can take a set of equally-spaced points in any given direction without approaching any point.
447:– that is, in a neighborhood of each point – into corresponding statements that hold throughout the space, and many theorems are of this character. 3061:
but this cover does not have a finite subcover. Here, the sets are open in the subspace topology even though they are not open as subsets of 
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Bourbaki defines a compact space (quasi-compact space) as a topological space where each filter has a cluster point (i.e., 8. in the above).
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must be in the space itself — an open (or half-open) interval of the real numbers is not compact. It is also crucial that the interval be
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coming from solutions of integral equations, Schmidt had shown that a property analogous to the Arzelà–Ascoli theorem held in the sense of
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be compact, since it contains both infinities. There are many ways to make this heuristic notion precise. These ways usually agree in a
431:" the space in the sense that each point of the space lies in some set contained in the family. This more subtle notion, introduced by 5578: 5191: 3108:
of all real numbers is not compact as there is a cover of open intervals that does not have a finite subcover. For example, intervals
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However, a different notion of compactness altogether had also slowly emerged at the end of the 19th century from the study of the
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Hausdorff spaces, form the abstract framework in which these spectra are studied. Such spaces are also useful in the study of
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arises in this manner, as the spectrum of some bounded linear operator. For instance, a diagonal operator on the Hilbert space
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is compact. This is not true for infinite dimensions; in fact, a normed vector space is finite-dimensional if and only if its
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to refer to this general phenomenon (he used the term already in his 1904 paper which led to the famous 1906 thesis).
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Koninklijke Nederlandse Akademie van Wetenschappen te Amsterdam, Proceedings of the Section of Mathematical Sciences
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is not Hausdorff then the intersection of two compact subsets may fail to be compact (see footnote for example).
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below). That this form of compactness holds for closed and bounded subsets of Euclidean space is known as the
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The intersection of any non-empty collection of compact subsets of a Hausdorff space is compact (and closed);
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In the 1880s, it became clear that results similar to the Bolzano–Weierstrass theorem could be formulated for
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accumulate to 0 (while others accumulate to 1). Since neither 0 nor 1 are members of the open unit interval
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On the other hand, the closed unit ball of the dual of a normed space is compact for the weak-* topology. (
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on an uncountable set, no infinite set is compact. Like the previous example, the space as a whole is not
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of the space is an open cover which admits no finite subcover. It is complete but not totally bounded.
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has a sub-base such that every cover of the space, by members of the sub-base, has a finite subcover (
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compact; note that the cover described above would never reach the points at infinity and thus would
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is not Hausdorff then the closure of a compact set may fail to be compact (see footnote for example).
2416: 1655: 1382: 900: 667:. If one chooses an infinite number of distinct points in the unit interval, then there must be some 578: 535: 230: 1435: 490:, and its method of proof, would not emerge until almost 50 years later when it was rediscovered by 94:. The idea is that a compact space has no "punctures" or "missing endpoints", i.e., it includes all 5506: 5302: 4889: 4750: 4730: 4624: 3856: 3685: 3456: 3402: 3192: 2800: 2796: 2792: 2199: 1647: 856: 792: 788: 574: 518: 514: 483: 412: 219: 95: 4098: 4044: 4017: 3985: 3953: 3662: 3611: 3589: 3303: 3228: 3135: 3089: 3064: 2820: 2814:
of the space is an open cover which admits no finite subcover. Finite discrete spaces are compact.
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Various definitions of compactness may apply, depending on the level of generality. A subset of
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is compact. Again from the Heine–Borel theorem, the closed unit ball of any finite-dimensional
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Hausdorff space can be turned into a compact space by adding a single point to it, by means of
890:. Compactness, when defined in this manner, often allows one to take information that is known 5593: 5488: 5354: 5312: 5177: 5115: 5088: 5074: 5006: 4944: 4903: 4893: 4764: 4716: 4608: 4410: 3891: 3876: 3871: 3758: 3710: 3370: 2855: 2707: 1835: 1677: 1375: 1367: 1349: 1345: 1114: 912: 867: 633: 632:, formulated Heine–Borel compactness in a way that could be applied to the modern notion of a 617: 523: 459: 237: 223: 184: 161: 130: 1877:(i.e. a totally ordered set equipped with the order topology), the following are equivalent: 5268: 5214: 5044: 4998: 4978: 4848: 4840: 4794: 4778: 4708: 4689: 4679: 4583: 3777: 3773: 3754: 3714: 3362: 3196: 2946: 2700: 2675: 2412: 2397: 2313: 2156: 1933: 1555: 1070: 875: 625: 566: 547: 539: 506: 491: 432: 428: 75: 5102: 5020: 4990: 4742: 4702: 395:
in 1906 to generalize the Bolzano–Weierstrass theorem from spaces of geometrical points to
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is an open dense subspace of a compact Hausdorff space having at most one point more than
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allows for the following alternative characterization of compactness: a topological space
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among these points in that interval. For instance, the odd-numbered terms of the sequence
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that converges to a point in the set. Various equivalent notions of compactness, such as
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is compact. In fact, every compact metric space is a continuous image of the Cantor set.
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An ordered space satisfying (any one of) these conditions is called a complete lattice.
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showed that the earlier version of compactness due to Fréchet, now called (relative)
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A collection of probability measures on the Borel sets of Euclidean space is called
569:, which was seen as fundamental for the rigorous formulation of analysis. In 1870, 558:, had distilled the essence of the Bolzano–Weierstrass property and coined the term 5412: 5332: 5278: 4932: 4754: 3837: 3826: 3739: 3732: 3580: 2540: 860: 570: 416: 215: 5087:(Dover Publications reprint of 1978 ed.). Berlin, New York: Springer-Verlag. 2354:
contains infinitesimals, which are infinitely close to 0, which is not a point of
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is closed and bounded (as a subset of any metric space whose restricted metric is
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from the real number line to the closed unit interval, and define a topology on
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In contrast, the different notions of compactness are not equivalent in general
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is not compact, because it has infinitely many "punctures" corresponding to the
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with the topology generated by the following basic open sets: every subset of
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is sometimes used as a synonym for compact space, but also often refers to a
17: 5391: 4907: 2692: 1849: 4982: 4915: 2699:(only finitely many open sets) is compact; this includes in particular the 1650:(also called weakly countably compact); that is, every infinite subset of 5376: 5344: 5293: 5200: 3185: 2217:
In general, for non-pseudocompact spaces there are always maximal ideals
1614: 1325: 934: 879: 513:, was a generalization of the Bolzano–Weierstrass theorem to families of 424: 2532:
A continuous bijection from a compact space into a Hausdorff space is a
517:, the precise conclusion of which was that it was possible to extract a 5137:
Sundström, Manya Raman (2010). "A pedagogical history of compactness".
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This property was significant because it allowed for the passage from
4607:. Encyclopedia of the Mathematical Sciences. Vol. 17. Springer. 1492: 5143: 5049: 4826: 4811:
Atti della R. Accad. Dei Lincei Memorie della Cl. Sci. Fis. Mat. Nat
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with an infinite number of points is compact. The collection of all
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is not compact because it is not closed (but bounded). The interval
589:), and it was generalized to arbitrary collections of intervals by 158:
is not compact either, because it excludes the two limiting values
37: 2126:{\displaystyle \operatorname {ev} _{p}\colon C(X)\to \mathbb {R} } 41:
Per the compactness criteria for Euclidean space as stated in the
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Leçons sur l'intégration et la recherche des fonctions primitives
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In addition, the following are equivalent for all ordered spaces
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as an offshoot of the general notion of a compact space. It was
3788:, "quasi" referring to the non-Hausdorff nature of the topology. 3357:. There is only one such topology; it is called the topology of 1856:
is closed and bounded but not compact, as the collection of all
870:, and the most useful notion of compactness – originally called 5173: 4927:. Graduate Texts in Mathematics. Vol. 27. Springer-Verlag. 4797:(1882–1883). "Un'osservazione intorno alle serie di funzioni". 1475:
Every open cover linearly ordered by subset inclusion contains
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is not compact: the sets of rational numbers in the intervals
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Mack, John (1967). "Directed covers and paracompact spaces".
4809:(1883–1884). "Le curve limiti di una varietà data di curve". 3780:(that is, the set of all prime ideals) is compact, but never 1848:). The converse may fail for a non-Euclidean space; e.g. the 1113:
is said to be compact if it is compact as a subspace (in the
423:— is phrased in terms of the existence of finite families of 1997:
Every decreasing nested sequence of nonempty closed subsets
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Every decreasing nested sequence of nonempty closed subsets
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The history of the calculus and its conceptual development
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are both compact subsets but their intersection, which is
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is a topological space then the following are equivalent:
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Rend. Dell' Accad. R. Delle Sci. dell'Istituto di Bologna
4590:(1929). "Mémoire sur les espaces topologiques compacts". 4125:
are compact open subsets, neither one of which is closed.
2930:{\textstyle \left({\frac {1}{n}},1-{\frac {1}{n}}\right)} 2400:
of any collection of compact spaces is compact. (This is
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cover the extended real line. In fact, the set has the
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Every increasing nested sequence of proper open subsets
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Every increasing nested sequence of proper open subsets
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is compact, again a consequence of Tychonoff's theorem.
3749:, and the quotient space is compact. This was used in 2944:
does not have a finite subcover. Similarly, the set of
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in 1929, exhibits compact spaces as generalizations of
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One such generalization is that a topological space is
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is a property that seeks to generalize the notion of a
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is not compact because it is not bounded. The interval
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is a compact topological space; this follows from the
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of a compact space having at most one point more than
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has no subsequence that converges to any real number.
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defined on a closed and bounded interval was in fact
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is not compact since the collection of open subsets
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is compact and Hausdorff, then no finer topology on
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Annales Scientifiques de l'École Normale Supérieure
1245:Compactness is a topological property. That is, if 4936: 4109: 4055: 4028: 3996: 3964: 3673: 3650: 3622: 3600: 3556: 3334: 3278: 3239: 3146: 3100: 3075: 3046: 2929: 2831: 2770: 2735: 2493:are disjoint compact subsets of a Hausdorff space 2426:A finite set endowed with any topology is compact. 2125: 1456: 1269: 1235: 1171: 1055: 991: 616:, who also exploited it in the development of the 376: 196: 173: 150: 121: 27:"Compactness" redirects here. For other uses, see 5037:Transactions of the American Mathematical Society 4939:Mathematical thought from ancient to modern times 4666:"Sur quelques points de la théorie des fonctions" 637: 542:– or convergence in what would later be dubbed a 240:of points sampled from the space has an infinite 66:is compact because it is both closed and bounded. 5164:Creative Commons Attribution/Share-Alike License 3688:on a compact Hausdorff space is compact for the 3557:{\displaystyle d(f,g)=\sup _{x\in }|f(x)-g(x)|.} 3487: 2695:, is compact. More generally, any space with a 1906:has an infimum (i.e. a greatest lower bound) in 1236:{\displaystyle K\subseteq \bigcup _{S\in F}S\ .} 1172:{\displaystyle K\subseteq \bigcup _{S\in C}S\ ,} 509:. The culmination of their investigations, the 4783:Mem. Accad. Sci. Ist. Bologna Cl. Sci. Fis. Mat 2350:is not compact because its hyperreal extension 1621:has a convergent subsequence whose limit is in 1069:, typically influenced by the French school of 384:(the real number line), the sequence of points 244:that converges to some point of the space. The 4506: 4186:be the set of non-negative integers. We endow 2367:A closed subset of a compact space is compact. 1944:is compact. (The converse in general fails if 1698:is an image of a continuous function from the 1089:. A compact set is sometimes referred to as a 5185: 4339: 1895:has a supremum (i.e. a least upper bound) in 1121:is compact if for every arbitrary collection 1077:for the general notion, and reserve the term 8: 4832:Rendiconti del Circolo Matematico di Palermo 4566: 4370: 4366:"Generalisation d'un theorem de Weierstrass" 4364: 3564:Then by the Arzelà–Ascoli theorem the space 3329: 3307: 3273: 3260: 2678:(i.e. all subsets have suprema and infima). 2651:has a greatest element and a least element. 1625:(this is also equivalent to compactness for 1595:(this is also equivalent to compactness for 1374:has a convergent subnet (see the article on 4827:"Sur quelques points du calcul fonctionnel" 4449:, § 10.2. Theorem 1, Corollary 1. 3735:to the Cantor set, they form a compact set. 2415:, a subset is compact if and only if it is 455: 5553: 5526: 5192: 5178: 5170: 2450:is not Hausdorff then a compact subset of 1281:equipped with the subspace topology, then 803:, one could choose the sequence of points 5142: 5048: 4943:(3rd ed.). Oxford University Press. 4868:Gillman, Leonard; Jerison, Meyer (1976). 4683: 4103: 4102: 4100: 4049: 4048: 4046: 4022: 4021: 4019: 3990: 3989: 3987: 3958: 3957: 3955: 3667: 3666: 3664: 3642: 3636: 3616: 3615: 3613: 3594: 3593: 3591: 3546: 3514: 3490: 3463: 3314: 3305: 3267: 3258: 3233: 3232: 3230: 3140: 3139: 3137: 3094: 3093: 3091: 3069: 3068: 3066: 3023: 3010: 3000: 2985: 2972: 2959: 2912: 2893: 2886: 2825: 2824: 2822: 2762: 2758: 2757: 2754: 2729: 2728: 2726: 2594:image of a compact space is compact, the 2119: 2118: 2094: 2088: 2069:the ring of real continuous functions on 1812:is contained in some member of the cover. 1786:also satisfies the following properties: 1680:; that is, every countable open cover of 1554:, the following are equivalent (assuming 1437: 1250: 1212: 1200: 1148: 1136: 1032: 1020: 968: 956: 831:in particular is called compact if it is 546:. This ultimately led to the notion of a 368: 364: 363: 360: 186: 163: 144: 143: 141: 115: 114: 112: 5154:This article incorporates material from 4518: 4470: 4446: 3795:is compact, a fact which is part of the 3659:may have any compact nonempty subset of 2210:has residue field the real numbers. For 2053:Characterization by continuous functions 1613:is sequentially compact; that is, every 613: 598: 5028:Scarborough, C.T.; Stone, A.H. (1966). 4763:(2nd ed.). John Wiley & Sons. 4494: 4258: 4063:is open; the only open sets containing 3930: 3745:is a discrete additive subgroup of its 2325:) has the property that every point of 1056:{\displaystyle X=\bigcup _{S\in F}S\ .} 992:{\displaystyle X=\bigcup _{S\in C}S\ ,} 555: 475: 391:Compactness was formally introduced by 4434: 4173:is a compact set but it is not closed. 2719:Alexandroff one-point compactification 2625:Alexandroff one-point compactification 2558:is compact and no coarser topology on 2497:, then there exist disjoint open sets 2256:is compact if and only if every point 2202:if and only if every maximal ideal in 1986:Every monotone decreasing sequence in 1975:Every monotone increasing sequence in 4422: 4351: 4335: 3047:{\textstyle \left{\text{ and }}\left} 2341:. For example, an open real interval 2331:is infinitely close to some point of 2190:is the field of real numbers, by the 1081:for topological spaces that are both 1065:Some branches of mathematics such as 586: 7: 4458: 4306: 4304: 4075:; and the only open sets containing 3717:are compact, while groups such as a 3608:. Conversely, any compact subset of 3583:is a nonempty compact subset of the 2749:; the one-point compactification of 2721:. The one-point compactification of 2381:image of a compact space is compact. 1964:has a subsequence that converges in 1917:has a maximum and a minimum element. 1355:Any collection of closed subsets of 620:. Ultimately, the Russian school of 5030:"Products of nearly compact spaces" 4781:(1895). "Sulle funzioni di linee". 4704:Topologie générale. Chapitres 1 à 4 4555:Arkhangel'skii & Fedorchuk 1990 4543:Arkhangel'skii & Fedorchuk 1990 4531:Arkhangel'skii & Fedorchuk 1990 4483:Arkhangel'skii & Fedorchuk 1990 2627:. By the same construction, every 1270:{\displaystyle K\subset Z\subset Y} 941:is compact if for every collection 2870:is compact. This follows from the 2454:may fail to be a closed subset of 2321:(constructed, for example, by the 791:points of the interval, since the 191: 168: 25: 4117:, is not compact. Note that both 2647:A nonempty compact subset of the 482:. Bolzano's proof relied on the 100:of points. For example, the open 5589:Properties of topological spaces 5552: 5525: 5515: 5505: 5494: 5484: 5483: 5277: 5068:from the original on 2017-08-16. 4737:. New York: Dover Publications. 4473:, § 9.1. Definition 1. 4246:does not have a finite subcover. 3161:carrying the analogous topology 3154:but there is no finite subcover. 3054:cover all the rationals in for 2843:, no uncountable set is compact. 2771:{\displaystyle \mathbb {R} ^{2}} 1913:Every nonempty closed subset of 1506:is compact if and only if it is 1414:converges to at least one point. 377:{\displaystyle \mathbb {R} ^{1}} 4971:Canadian Journal of Mathematics 4316:www-groups.mcs.st-andrews.ac.uk 4297:. Warsaw, PL: PWN. p. 266. 1990:converges to a unique limit in 1979:converges to a unique limit in 638:Alexandrov & Urysohn (1929) 5162:, which is licensed under the 5005:. Princeton University Press. 4892:Science & Business Media. 4623:Arkhangel'skii, A.V. (2001) , 4318:. MT 4522 course lectures 3547: 3543: 3537: 3528: 3522: 3515: 3509: 3497: 3480: 3468: 3326: 3320: 2778:is homeomorphic to the sphere 2743:is homeomorphic to the circle 2565:If a subset of a metric space 2115: 2112: 2106: 1457:{\displaystyle X\times Y\to Y} 1448: 859:, can be developed in general 1: 4886:Graduate Texts in Mathematics 4870:Rings of continuous functions 3822:is a compact Hausdorff space. 2539:A compact Hausdorff space is 2404:, which is equivalent to the 2155:is a ring homomorphism. The 618:integral now bearing his name 4882:Modern Analysis and Topology 4110:{\displaystyle \mathbb {N} } 4056:{\displaystyle \mathbb {N} } 4029:{\displaystyle \mathbb {N} } 3997:{\displaystyle \mathbb {N} } 3965:{\displaystyle \mathbb {N} } 3882:Noetherian topological space 3797:Stone representation theorem 3674:{\displaystyle \mathbb {C} } 3623:{\displaystyle \mathbb {C} } 3601:{\displaystyle \mathbb {C} } 3335:{\displaystyle \{f_{n}(x)\}} 3240:{\displaystyle \mathbb {R} } 3147:{\displaystyle \mathbb {R} } 3126:takes all integer values in 3101:{\displaystyle \mathbb {R} } 3076:{\displaystyle \mathbb {R} } 2832:{\displaystyle \mathbb {R} } 2736:{\displaystyle \mathbb {R} } 2586:Functions and compact spaces 2431:Properties of compact spaces 2229:such that the residue field 2019:has a nonempty intersection. 1734:has a nonempty intersection. 1428:For every topological space 1389:has a convergent refinement. 1361:finite intersection property 1336:Alexander's sub-base theorem 415:, were developed in general 151:{\displaystyle \mathbb {R} } 122:{\displaystyle \mathbb {Q} } 29:Compactness (disambiguation) 5084:Counterexamples in Topology 4630:Encyclopedia of Mathematics 4293:Engelking, Ryszard (1977). 4282:– via britannica.com. 4218:is compact, the closure of 3913:Relatively compact subspace 2799:is compact. In particular, 2474:(TVS), a compact subset is 2458:(see footnote for example). 2374:of compact sets is compact. 2061:be a topological space and 1423:complete accumulation point 841:Bolzano–Weierstrass theorem 246:Bolzano–Weierstrass theorem 5610: 5446:Banach fixed-point theorem 5156:Examples of compact spaces 4701:Bourbaki, Nicolas (2007). 4507:Gillman & Jerison 1976 4409:Here, "collection" means " 4204:to be open if and only if 3867:Exhaustion by compact sets 3455:the metric induced by the 2670:is compact if and only if 1952:is not also metrizable.): 1804:such that every subset of 1793:: For every open cover of 1363:has nonempty intersection. 810:In two dimensions, closed 534:. For a certain class of 34:Type of mathematical space 26: 5579:Compactness (mathematics) 5479: 5275: 5110:Willard, Stephen (1970). 4713:10.1007/978-3-540-33982-3 4365: 4340:Boyer & Merzbach 1991 4192:particular point topology 3852:Compactly generated space 3692:, by the Alaoglu theorem. 3651:{\displaystyle \ell ^{2}} 3279:{\displaystyle \{f_{n}\}} 3159:extended real number line 2260:of the natural extension 2212:completely regular spaces 2192:first isomorphism theorem 1417:Every infinite subset of 624:, under the direction of 4958:Lebesgue, Henri (1904). 4760:A History of Mathematics 4567:Steen & Seebach 1995 4312:"Sequential compactness" 4272:Encyclopaedia Britannica 3818:of a commutative unital 2689:finite topological space 2611:Every topological space 2472:topological vector space 1797:, there exists a number 1316:is compact; i.e., every 799:, since in the interval 197:{\displaystyle -\infty } 174:{\displaystyle +\infty } 4425:, pp. xxvi–xxviii. 3577:bounded linear operator 3157:On the other hand, the 2950:in the closed interval 2706:Any space carrying the 2323:ultrapower construction 1791:Lebesgue's number lemma 1774:A compact metric space 1109:of a topological space 857:limit point compactness 839:. This implies, by the 413:limit point compactness 405:Peano existence theorem 5501:Mathematics portal 5401:Metrics and properties 5387:Second-countable space 5114:. Dover publications. 5079:Seebach, J. Arthur Jr. 4983:10.4153/CJM-1967-059-0 4371: 4111: 4057: 4030: 3998: 3966: 3897:Quasi-compact morphism 3675: 3652: 3624: 3602: 3558: 3336: 3280: 3241: 3148: 3102: 3077: 3048: 2931: 2833: 2772: 2737: 2643:Ordered compact spaces 2577:is compact then it is 2436:A compact subset of a 2194:. A topological space 2127: 1684:has a finite subcover. 1458: 1271: 1237: 1173: 1101:Compactness of subsets 1057: 993: 853:sequential compactness 642:sequential compactness 466:Historical development 409:sequential compactness 378: 198: 175: 152: 123: 67: 5003:Non-standard analysis 4923:Kelley, John (1955). 4521:, Theorem 4.1.13 4194:by defining a subset 4112: 4058: 4031: 3999: 3967: 3676: 3653: 3625: 3603: 3559: 3378:Arzelà–Ascoli theorem 3359:pointwise convergence 3353:for all real numbers 3337: 3281: 3242: 3149: 3103: 3078: 3049: 2932: 2834: 2773: 2738: 2662:set endowed with the 2596:extreme value theorem 2362:Sufficient conditions 2250:non-standard analysis 2128: 2083:, the evaluation map 1869:For an ordered space 1542:For any metric space 1459: 1272: 1238: 1174: 1058: 994: 907:Open cover definition 884:Open cover definition 526:, as investigated by 511:Arzelà–Ascoli theorem 401:Arzelà–Ascoli theorem 379: 199: 176: 153: 124: 40: 5456:Invariance of domain 5408:Euler characteristic 5382:Bundle (mathematics) 4751:Boyer, Carl Benjamin 4707:. Berlin: Springer. 4651:. Wilhelm Engelmann. 4485:, Theorem 5.3.7 4372:Analyse Mathematique 4338:, pp. 952–953; 4099: 4045: 4018: 3986: 3954: 3805:totally disconnected 3719:general linear group 3686:probability measures 3663: 3635: 3612: 3590: 3462: 3425:| ≤ | 3304: 3257: 3229: 3136: 3090: 3065: 2958: 2885: 2878:is not compact: the 2874:. The open interval 2848:cocountable topology 2841:lower limit topology 2821: 2789:right order topology 2753: 2725: 2417:sequentially compact 2304:Hyperreal definition 2287:is contained in the 2087: 1936:) are true whenever 1436: 1403:has a cluster point. 1396:has a cluster point. 1249: 1199: 1135: 1019: 955: 901:uniformly continuous 843:, that any infinite 579:uniformly continuous 519:uniformly convergent 515:continuous functions 359: 185: 162: 140: 111: 5466:Tychonoff's theorem 5461:Poincaré conjecture 5215:General (point-set) 4964:. Gauthier-Villars. 4385:Weisstein, Eric W. 3857:Compactness theorem 3684:The space of Borel 3403:Lipschitz condition 3253:so that a sequence 3193:normed vector space 2872:Heine–Borel theorem 2797:totally ordered set 2793:left order topology 2402:Tychonoff's theorem 2314:hyperreal extension 2248:. The framework of 1648:limit point compact 1516:Heine–Borel theorem 1125:of open subsets of 945:of open subsets of 888:Heine–Borel theorem 874:– is defined using 847:from the set has a 603:Heine–Borel theorem 575:continuous function 499:spaces of functions 484:method of bisection 397:spaces of functions 133:, and the space of 43:Heine–Borel theorem 5451:De Rham cohomology 5372:Polyhedral complex 5362:Simplicial complex 5075:Steen, Lynn Arthur 4872:. Springer-Verlag. 4853:10338.dmlcz/100655 4845:10.1007/BF03018603 4685:10.24033/asens.406 4605:General Topology I 4497:Theorem 30.7. 4363:Frechet, M. 1904. 4153:with the topology 4107: 4053: 4026: 3994: 3962: 3887:Orthocompact space 3862:Eberlein compactum 3791:The spectrum of a 3711:Topological groups 3705:Algebraic examples 3671: 3648: 3620: 3598: 3554: 3513: 3342:converges towards 3332: 3290:converges towards 3276: 3237: 3144: 3098: 3073: 3044: 2927: 2829: 2768: 2733: 2312:is compact if its 2123: 1956:Every sequence in 1852:equipped with the 1454: 1267: 1233: 1223: 1169: 1159: 1067:algebraic geometry 1053: 1043: 989: 979: 868:topological spaces 669:accumulation point 622:point-set topology 524:integral equations 386:0,  1,  2,  3, ... 374: 224:topological spaces 194: 171: 148: 131:irrational numbers 119: 68: 5566: 5565: 5355:fundamental group 5094:978-0-486-68735-3 5012:978-0-691-04490-3 4999:Robinson, Abraham 4950:978-0-19-506136-9 4899:978-0-387-97986-1 4770:978-0-471-54397-8 4722:978-3-540-33982-3 4614:978-0-387-18178-3 4584:Alexandrov, Pavel 4557:, Corollary 5.2.1 4391:Wolfram MathWorld 3892:Paracompact space 3877:Metacompact space 3759:harmonic analysis 3486: 3387:of all functions 3383:Consider the set 3371:Tychonoff theorem 3220:of all functions 3216:Consider the set 3204:Alaoglu's theorem 3031: 3018: 3003: 2993: 2980: 2920: 2901: 2708:cofinite topology 2607:Compactifications 2283:(more precisely, 1808:of diameter < 1678:countably compact 1654:has at least one 1432:, the projection 1350:countably compact 1229: 1208: 1165: 1144: 1115:subspace topology 1049: 1028: 985: 964: 913:topological space 634:topological space 610:local information 536:Green's functions 488:Bolzano's theorem 460:topological space 238:infinite sequence 218:, but may not be 16:(Redirected from 5601: 5584:General topology 5556: 5555: 5529: 5528: 5519: 5509: 5499: 5498: 5487: 5486: 5281: 5194: 5187: 5180: 5171: 5148: 5146: 5125: 5112:General Topology 5106: 5069: 5067: 5052: 5034: 5024: 4994: 4965: 4954: 4942: 4928: 4925:General topology 4919: 4880:(23 June 1995). 4878:Howes, Norman R. 4873: 4864: 4823:Fréchet, Maurice 4818: 4802: 4790: 4774: 4746: 4726: 4697: 4687: 4652: 4643:Bolzano, Bernard 4637: 4618: 4599: 4570: 4564: 4558: 4552: 4546: 4540: 4534: 4528: 4522: 4516: 4510: 4504: 4498: 4492: 4486: 4480: 4474: 4468: 4462: 4456: 4450: 4444: 4438: 4432: 4426: 4420: 4414: 4407: 4401: 4400: 4398: 4397: 4382: 4376: 4374: 4368: 4367: 4361: 4355: 4354:, Chapter 46, §2 4349: 4343: 4333: 4327: 4326: 4324: 4323: 4308: 4299: 4298: 4295:General Topology 4290: 4284: 4283: 4281: 4280: 4263: 4247: 4245: 4229: 4225: 4221: 4217: 4210: 4203: 4189: 4185: 4180: 4174: 4172: 4164: 4152: 4148: 4132: 4126: 4124: 4120: 4116: 4114: 4113: 4108: 4106: 4094: 4090: 4086: 4082: 4078: 4074: 4070: 4066: 4062: 4060: 4059: 4054: 4052: 4040: 4036: 4035: 4033: 4032: 4027: 4025: 4004: 4003: 4001: 4000: 3995: 3993: 3972: 3971: 3969: 3968: 3963: 3961: 3935: 3809:profinite groups 3778:Zariski topology 3774:commutative ring 3728: 3715:orthogonal group 3680: 3678: 3677: 3672: 3670: 3657: 3655: 3654: 3649: 3647: 3646: 3629: 3627: 3626: 3621: 3619: 3607: 3605: 3604: 3599: 3597: 3567: 3563: 3561: 3560: 3555: 3550: 3518: 3512: 3457:uniform distance 3454: 3450: 3449: 3436: 3434: 3424: 3400: 3399: 3395: 3386: 3368: 3363:product topology 3356: 3352: 3341: 3339: 3338: 3333: 3319: 3318: 3299: 3289: 3285: 3283: 3282: 3277: 3272: 3271: 3252: 3248: 3246: 3244: 3243: 3238: 3236: 3219: 3197:closed unit ball 3188: 3183: 3153: 3151: 3150: 3145: 3143: 3131: 3125: 3121: 3120: 3118: 3114: 3107: 3105: 3104: 3099: 3097: 3082: 3080: 3079: 3074: 3072: 3060: 3058: 3053: 3051: 3050: 3045: 3043: 3039: 3032: 3024: 3019: 3011: 3004: 3001: 2999: 2995: 2994: 2986: 2981: 2973: 2953: 2947:rational numbers 2943: 2941: 2936: 2934: 2933: 2928: 2926: 2922: 2921: 2913: 2902: 2894: 2877: 2869: 2868: 2838: 2836: 2835: 2830: 2828: 2801:Sierpiński space 2783: 2777: 2775: 2774: 2769: 2767: 2766: 2761: 2748: 2742: 2740: 2739: 2734: 2732: 2701:trivial topology 2691:, including the 2676:complete lattice 2673: 2669: 2657: 2638: 2634: 2631:Hausdorff space 2622: 2614: 2580: 2576: 2561: 2557: 2553: 2528: 2518: 2508: 2504: 2500: 2496: 2492: 2488: 2464: 2457: 2453: 2449: 2442: 2421:countable choice 2413:metrizable space 2390: 2357: 2353: 2349: 2348: 2340: 2330: 2320: 2311: 2299: 2286: 2282: 2278: 2268:infinitely close 2265: 2259: 2255: 2239: 2228: 2220: 2209: 2197: 2189: 2188: 2167: 2154: 2132: 2130: 2129: 2124: 2122: 2099: 2098: 2082: 2072: 2068: 2060: 2047: 2043: 2032: 2025: 2018: 2007: 2000: 1993: 1989: 1982: 1978: 1971: 1963: 1951: 1943: 1934:countable choice 1932:, and (assuming 1931: 1916: 1909: 1905: 1902:Every subset of 1898: 1894: 1891:Every subset of 1887: 1876: 1847: 1843: 1828:second-countable 1825: 1811: 1807: 1803: 1796: 1785: 1769: 1765: 1753: 1733: 1721: 1697: 1683: 1675: 1661: 1653: 1645: 1624: 1620: 1612: 1586: 1572: 1556:countable choice 1553: 1533: 1505: 1497: 1478: 1463: 1461: 1460: 1455: 1431: 1420: 1413: 1402: 1399:Every filter on 1395: 1388: 1373: 1358: 1343: 1333: 1323: 1315: 1308: 1301:Characterization 1296: 1292: 1288: 1284: 1280: 1276: 1274: 1273: 1268: 1242: 1240: 1239: 1234: 1227: 1222: 1192: 1188: 1178: 1176: 1175: 1170: 1163: 1158: 1128: 1124: 1120: 1112: 1108: 1062: 1060: 1059: 1054: 1047: 1042: 1012: 1008: 998: 996: 995: 990: 983: 978: 948: 944: 940: 929: 917: 806: 802: 786: 784: 782: 781: 778: 775: 768: 766: 765: 762: 759: 752: 750: 749: 746: 743: 736: 734: 733: 730: 727: 720: 718: 717: 714: 711: 704: 702: 701: 698: 695: 688: 686: 685: 682: 679: 662: 626:Pavel Alexandrov 548:compact operator 540:mean convergence 492:Karl Weierstrass 456:compact subspace 433:Pavel Alexandrov 387: 383: 381: 380: 375: 373: 372: 367: 354: 350: 348: 346: 345: 342: 339: 332: 330: 329: 326: 323: 316: 314: 313: 310: 307: 300: 298: 297: 294: 291: 284: 282: 281: 278: 275: 268: 266: 265: 262: 259: 209:real number line 203: 201: 200: 195: 180: 178: 177: 172: 157: 155: 154: 149: 147: 128: 126: 125: 120: 118: 106:rational numbers 76:general topology 65: 58: 51: 21: 5609: 5608: 5604: 5603: 5602: 5600: 5599: 5598: 5569: 5568: 5567: 5562: 5493: 5475: 5471:Urysohn's lemma 5432: 5396: 5282: 5273: 5245:low-dimensional 5203: 5198: 5151: 5136: 5133: 5128: 5122: 5109: 5095: 5073: 5065: 5050:10.2307/1994440 5032: 5027: 5013: 4997: 4968: 4957: 4951: 4931: 4922: 4900: 4890:Springer-Verlag 4876: 4867: 4821: 4805: 4793: 4777: 4771: 4755:Merzbach, Uta C 4749: 4729: 4723: 4700: 4660: 4641: 4625:"Compact space" 4622: 4615: 4602: 4582: 4578: 4573: 4565: 4561: 4553: 4549: 4545:, Theorem 5.2.2 4541: 4537: 4533:, Theorem 5.2.3 4529: 4525: 4517: 4513: 4505: 4501: 4493: 4489: 4481: 4477: 4469: 4465: 4457: 4453: 4445: 4441: 4433: 4429: 4421: 4417: 4408: 4404: 4395: 4393: 4387:"Compact Space" 4384: 4383: 4379: 4362: 4358: 4350: 4346: 4334: 4330: 4321: 4319: 4310: 4309: 4302: 4292: 4291: 4287: 4278: 4276: 4265: 4264: 4260: 4256: 4251: 4250: 4231: 4227: 4223: 4219: 4212: 4205: 4195: 4187: 4183: 4181: 4177: 4166: 4154: 4150: 4135: 4133: 4129: 4122: 4118: 4097: 4096: 4092: 4088: 4084: 4080: 4076: 4072: 4068: 4064: 4043: 4042: 4038: 4016: 4015: 4006: 3984: 3983: 3974: 3952: 3951: 3938: 3936: 3932: 3927: 3922: 3918:Totally bounded 3907:totally bounded 3847: 3834:profinite group 3816:structure space 3793:Boolean algebra 3726: 3707: 3661: 3660: 3638: 3633: 3632: 3610: 3609: 3588: 3587: 3585:complex numbers 3565: 3460: 3459: 3452: 3451:. Consider on 3447: 3438: 3426: 3407: 3405: 3401:satisfying the 3397: 3393: 3388: 3384: 3366: 3354: 3343: 3310: 3302: 3301: 3300:if and only if 3291: 3287: 3263: 3255: 3254: 3250: 3227: 3226: 3221: 3217: 3186: 3181: 3134: 3133: 3127: 3123: 3116: 3112: 3110: 3109: 3088: 3087: 3063: 3062: 3056: 3055: 3009: 3005: 3002: and  2965: 2961: 2956: 2955: 2951: 2939: 2938: 2892: 2888: 2883: 2882: 2875: 2866: 2865: 2852:locally compact 2819: 2818: 2795:on any bounded 2779: 2756: 2751: 2750: 2744: 2723: 2722: 2715:locally compact 2697:finite topology 2684: 2671: 2667: 2655: 2645: 2636: 2632: 2629:locally compact 2620: 2612: 2609: 2588: 2578: 2566: 2559: 2555: 2551: 2520: 2510: 2506: 2502: 2498: 2494: 2490: 2486: 2462: 2455: 2451: 2447: 2440: 2438:Hausdorff space 2433: 2406:axiom of choice 2388: 2364: 2355: 2351: 2343: 2342: 2332: 2326: 2316: 2309: 2306: 2298: 2292: 2284: 2280: 2277: 2271: 2261: 2257: 2253: 2246:hyperreal field 2242:non-Archimedean 2230: 2222: 2218: 2203: 2195: 2187: 2177: 2176: 2166: 2160: 2140: 2134: 2090: 2085: 2084: 2074: 2070: 2062: 2058: 2055: 2045: 2044:fails to cover 2037: 2035: 2030: 2028: 2023: 2012: 2010: 2005: 2003: 1998: 1991: 1987: 1980: 1976: 1965: 1957: 1945: 1937: 1925: 1914: 1907: 1903: 1896: 1892: 1881: 1870: 1867: 1854:discrete metric 1845: 1841: 1815: 1809: 1805: 1798: 1794: 1775: 1767: 1766:fails to cover 1755: 1751: 1744: 1738: 1723: 1719: 1712: 1706: 1687: 1681: 1665: 1659: 1651: 1635: 1627:first-countable 1622: 1618: 1602: 1593:totally bounded 1576: 1562: 1543: 1540: 1531: 1523:Euclidean space 1503: 1500:Euclidean space 1495: 1489: 1487:Euclidean space 1476: 1434: 1433: 1429: 1418: 1411: 1400: 1393: 1386: 1371: 1356: 1341: 1331: 1321: 1313: 1306: 1303: 1294: 1290: 1289:if and only if 1286: 1282: 1278: 1247: 1246: 1197: 1196: 1190: 1186: 1133: 1132: 1126: 1122: 1118: 1110: 1106: 1103: 1073:, use the term 1017: 1016: 1010: 1006: 953: 952: 946: 942: 938: 927: 915: 909: 829:Euclidean space 825: 805:0, 1, 2, 3, ... 804: 800: 779: 776: 773: 772: 770: 763: 760: 757: 756: 754: 747: 744: 741: 740: 738: 731: 728: 725: 724: 722: 715: 712: 709: 708: 706: 699: 696: 693: 692: 690: 683: 680: 677: 676: 674: 672: 660: 650: 614:Lebesgue (1904) 552:Maurice Fréchet 472:Bernard Bolzano 468: 393:Maurice Fréchet 385: 362: 357: 356: 352: 343: 340: 337: 336: 334: 327: 324: 321: 320: 318: 311: 308: 305: 304: 302: 295: 292: 289: 288: 286: 279: 276: 273: 272: 270: 263: 260: 257: 256: 254: 253: 204:. However, the 183: 182: 160: 159: 138: 137: 109: 108: 97:limiting values 92:Euclidean space 74:, specifically 60: 53: 46: 45:, the interval 35: 32: 23: 22: 15: 12: 11: 5: 5607: 5605: 5597: 5596: 5591: 5586: 5581: 5571: 5570: 5564: 5563: 5561: 5560: 5550: 5549: 5548: 5543: 5538: 5523: 5513: 5503: 5491: 5480: 5477: 5476: 5474: 5473: 5468: 5463: 5458: 5453: 5448: 5442: 5440: 5434: 5433: 5431: 5430: 5425: 5420: 5418:Winding number 5415: 5410: 5404: 5402: 5398: 5397: 5395: 5394: 5389: 5384: 5379: 5374: 5369: 5364: 5359: 5358: 5357: 5352: 5350:homotopy group 5342: 5341: 5340: 5335: 5330: 5325: 5320: 5310: 5305: 5300: 5290: 5288: 5284: 5283: 5276: 5274: 5272: 5271: 5266: 5261: 5260: 5259: 5249: 5248: 5247: 5237: 5232: 5227: 5222: 5217: 5211: 5209: 5205: 5204: 5199: 5197: 5196: 5189: 5182: 5174: 5150: 5149: 5132: 5131:External links 5129: 5127: 5126: 5120: 5107: 5093: 5071: 5043:(1): 131–147. 5025: 5011: 4995: 4966: 4955: 4949: 4929: 4920: 4898: 4874: 4865: 4819: 4803: 4795:Arzelà, Cesare 4791: 4779:Arzelà, Cesare 4775: 4769: 4747: 4731:Boyer, Carl B. 4727: 4721: 4698: 4658: 4639: 4620: 4613: 4600: 4588:Urysohn, Pavel 4579: 4577: 4574: 4572: 4571: 4559: 4547: 4535: 4523: 4511: 4499: 4487: 4475: 4463: 4451: 4439: 4427: 4415: 4402: 4377: 4356: 4344: 4328: 4300: 4285: 4257: 4255: 4252: 4249: 4248: 4175: 4127: 4105: 4051: 4024: 3992: 3960: 3929: 3928: 3926: 3923: 3921: 3920: 3915: 3910: 3904:- also called 3902:Precompact set 3899: 3894: 3889: 3884: 3879: 3874: 3872:Lindelöf space 3869: 3864: 3859: 3854: 3848: 3846: 3843: 3842: 3841: 3830: 3823: 3820:Banach algebra 3812: 3789: 3766: 3761:to be used in 3736: 3729:-adic integers 3722: 3706: 3703: 3702: 3701: 3693: 3690:vague topology 3682: 3669: 3645: 3641: 3618: 3596: 3569: 3553: 3549: 3545: 3542: 3539: 3536: 3533: 3530: 3527: 3524: 3521: 3517: 3511: 3508: 3505: 3502: 3499: 3496: 3493: 3489: 3485: 3482: 3479: 3476: 3473: 3470: 3467: 3415:) −  3398:[0, 1] 3394:[0, 1] 3381: 3374: 3331: 3328: 3325: 3322: 3317: 3313: 3309: 3275: 3270: 3266: 3262: 3235: 3214: 3207: 3200: 3179:natural number 3175: 3155: 3142: 3096: 3084: 3071: 3042: 3038: 3035: 3030: 3027: 3022: 3017: 3014: 3008: 2998: 2992: 2989: 2984: 2979: 2976: 2971: 2968: 2964: 2925: 2919: 2916: 2911: 2908: 2905: 2900: 2897: 2891: 2867:[0, 1] 2859: 2844: 2827: 2815: 2808:discrete space 2804: 2785: 2765: 2760: 2731: 2711: 2704: 2683: 2680: 2664:order topology 2660:simply ordered 2644: 2641: 2617:dense subspace 2608: 2605: 2587: 2584: 2583: 2582: 2563: 2548: 2537: 2530: 2483: 2468: 2467: 2466: 2459: 2432: 2429: 2428: 2427: 2424: 2409: 2394: 2393: 2392: 2382: 2375: 2368: 2363: 2360: 2305: 2302: 2296: 2275: 2183: 2162: 2136: 2121: 2117: 2114: 2111: 2108: 2105: 2102: 2097: 2093: 2054: 2051: 2050: 2049: 2033: 2026: 2020: 2008: 2001: 1995: 1984: 1973: 1919: 1918: 1911: 1900: 1889: 1866: 1865:Ordered spaces 1863: 1862: 1861: 1839: 1813: 1772: 1771: 1749: 1742: 1735: 1717: 1710: 1703: 1685: 1663: 1633: 1630:uniform spaces 1600: 1597:uniform spaces 1574: 1539: 1536: 1514:; this is the 1488: 1485: 1481: 1480: 1473: 1466:closed mapping 1453: 1450: 1447: 1444: 1441: 1426: 1415: 1404: 1397: 1390: 1379: 1364: 1353: 1339: 1329: 1302: 1299: 1293:is compact in 1285:is compact in 1277:, with subset 1266: 1263: 1260: 1257: 1254: 1232: 1226: 1221: 1218: 1215: 1211: 1207: 1204: 1185:subcollection 1168: 1162: 1157: 1154: 1151: 1147: 1143: 1140: 1102: 1099: 1052: 1046: 1041: 1038: 1035: 1031: 1027: 1024: 1005:subcollection 988: 982: 977: 974: 971: 967: 963: 960: 908: 905: 878:consisting of 824: 821: 649: 648:Basic examples 646: 595:Henri Lebesgue 573:showed that a 532:Erhard Schmidt 467: 464: 371: 366: 193: 190: 170: 167: 146: 117: 33: 24: 14: 13: 10: 9: 6: 4: 3: 2: 5606: 5595: 5592: 5590: 5587: 5585: 5582: 5580: 5577: 5576: 5574: 5559: 5551: 5547: 5544: 5542: 5539: 5537: 5534: 5533: 5532: 5524: 5522: 5518: 5514: 5512: 5508: 5504: 5502: 5497: 5492: 5490: 5482: 5481: 5478: 5472: 5469: 5467: 5464: 5462: 5459: 5457: 5454: 5452: 5449: 5447: 5444: 5443: 5441: 5439: 5435: 5429: 5428:Orientability 5426: 5424: 5421: 5419: 5416: 5414: 5411: 5409: 5406: 5405: 5403: 5399: 5393: 5390: 5388: 5385: 5383: 5380: 5378: 5375: 5373: 5370: 5368: 5365: 5363: 5360: 5356: 5353: 5351: 5348: 5347: 5346: 5343: 5339: 5336: 5334: 5331: 5329: 5326: 5324: 5321: 5319: 5316: 5315: 5314: 5311: 5309: 5306: 5304: 5301: 5299: 5295: 5292: 5291: 5289: 5285: 5280: 5270: 5267: 5265: 5264:Set-theoretic 5262: 5258: 5255: 5254: 5253: 5250: 5246: 5243: 5242: 5241: 5238: 5236: 5233: 5231: 5228: 5226: 5225:Combinatorial 5223: 5221: 5218: 5216: 5213: 5212: 5210: 5206: 5202: 5195: 5190: 5188: 5183: 5181: 5176: 5175: 5172: 5168: 5167: 5165: 5161: 5157: 5145: 5140: 5135: 5134: 5130: 5123: 5121:0-486-43479-6 5117: 5113: 5108: 5104: 5100: 5096: 5090: 5086: 5085: 5080: 5076: 5072: 5064: 5060: 5056: 5051: 5046: 5042: 5038: 5031: 5026: 5022: 5018: 5014: 5008: 5004: 5000: 4996: 4992: 4988: 4984: 4980: 4976: 4972: 4967: 4963: 4962: 4956: 4952: 4946: 4941: 4940: 4934: 4933:Kline, Morris 4930: 4926: 4921: 4917: 4913: 4909: 4905: 4901: 4895: 4891: 4887: 4883: 4879: 4875: 4871: 4866: 4862: 4858: 4854: 4850: 4846: 4842: 4838: 4834: 4833: 4828: 4824: 4820: 4817:(3): 521–586. 4816: 4812: 4808: 4804: 4800: 4796: 4792: 4788: 4784: 4780: 4776: 4772: 4766: 4762: 4761: 4756: 4752: 4748: 4744: 4740: 4736: 4732: 4728: 4724: 4718: 4714: 4710: 4706: 4705: 4699: 4695: 4691: 4686: 4681: 4677: 4673: 4672: 4667: 4663: 4659: 4656: 4650: 4649: 4644: 4640: 4636: 4632: 4631: 4626: 4621: 4616: 4610: 4606: 4601: 4597: 4593: 4589: 4585: 4581: 4580: 4575: 4568: 4563: 4560: 4556: 4551: 4548: 4544: 4539: 4536: 4532: 4527: 4524: 4520: 4519:Robinson 1996 4515: 4512: 4508: 4503: 4500: 4496: 4491: 4488: 4484: 4479: 4476: 4472: 4471:Bourbaki 2007 4467: 4464: 4460: 4455: 4452: 4448: 4447:Bourbaki 2007 4443: 4440: 4437:, p. 163 4436: 4431: 4428: 4424: 4419: 4416: 4412: 4406: 4403: 4392: 4388: 4381: 4378: 4373: 4360: 4357: 4353: 4348: 4345: 4342:, p. 561 4341: 4337: 4332: 4329: 4317: 4313: 4307: 4305: 4301: 4296: 4289: 4286: 4275:. mathematics 4274: 4273: 4268: 4267:"Compactness" 4262: 4259: 4253: 4243: 4239: 4235: 4215: 4209: 4202: 4198: 4193: 4179: 4176: 4170: 4162: 4158: 4146: 4142: 4138: 4131: 4128: 4013: 4009: 3981: 3977: 3949: 3945: 3941: 3934: 3931: 3924: 3919: 3916: 3914: 3911: 3909: 3908: 3903: 3900: 3898: 3895: 3893: 3890: 3888: 3885: 3883: 3880: 3878: 3875: 3873: 3870: 3868: 3865: 3863: 3860: 3858: 3855: 3853: 3850: 3849: 3844: 3840:) is compact. 3839: 3835: 3831: 3828: 3824: 3821: 3817: 3813: 3810: 3806: 3802: 3798: 3794: 3790: 3787: 3783: 3779: 3775: 3771: 3767: 3764: 3763:number theory 3760: 3756: 3752: 3748: 3744: 3741: 3737: 3734: 3730: 3723: 3720: 3716: 3712: 3709: 3708: 3704: 3698: 3694: 3691: 3687: 3683: 3658: 3643: 3639: 3586: 3582: 3578: 3574: 3570: 3551: 3540: 3534: 3531: 3525: 3519: 3506: 3503: 3500: 3494: 3491: 3483: 3477: 3474: 3471: 3465: 3458: 3448:[0,1] 3446: ∈  3445: 3441: 3433: 3430: −  3429: 3422: 3418: 3414: 3410: 3404: 3391: 3382: 3379: 3375: 3372: 3364: 3360: 3350: 3346: 3323: 3315: 3311: 3298: 3294: 3268: 3264: 3224: 3215: 3212: 3208: 3205: 3201: 3198: 3194: 3190: 3180: 3176: 3172: 3171:homeomorphism 3168: 3164: 3160: 3156: 3130: 3085: 3040: 3036: 3033: 3028: 3025: 3020: 3015: 3012: 3006: 2996: 2990: 2987: 2982: 2977: 2974: 2969: 2966: 2962: 2952:[0,1] 2949: 2948: 2923: 2917: 2914: 2909: 2906: 2903: 2898: 2895: 2889: 2881: 2873: 2864: 2863:unit interval 2860: 2857: 2854:but is still 2853: 2849: 2845: 2842: 2839:carrying the 2816: 2813: 2809: 2805: 2802: 2798: 2794: 2790: 2786: 2782: 2763: 2747: 2720: 2716: 2712: 2709: 2705: 2702: 2698: 2694: 2690: 2686: 2685: 2681: 2679: 2677: 2665: 2661: 2652: 2650: 2642: 2640: 2630: 2626: 2618: 2606: 2604: 2602: 2597: 2593: 2585: 2574: 2570: 2564: 2562:is Hausdorff. 2549: 2546: 2542: 2538: 2535: 2534:homeomorphism 2531: 2527: 2523: 2517: 2513: 2484: 2481: 2477: 2473: 2469: 2460: 2445: 2444: 2439: 2435: 2434: 2430: 2425: 2422: 2418: 2414: 2410: 2407: 2403: 2399: 2395: 2386: 2385: 2383: 2380: 2376: 2373: 2369: 2366: 2365: 2361: 2359: 2346: 2339: 2335: 2329: 2324: 2319: 2315: 2303: 2301: 2295: 2290: 2274: 2269: 2264: 2251: 2247: 2243: 2238: 2234: 2226: 2215: 2213: 2207: 2201: 2200:pseudocompact 2193: 2186: 2181: 2175: 2174:residue field 2171: 2170:maximal ideal 2165: 2158: 2152: 2148: 2144: 2139: 2109: 2103: 2100: 2095: 2091: 2081: 2077: 2066: 2052: 2041: 2021: 2016: 1996: 1985: 1974: 1969: 1961: 1955: 1954: 1953: 1949: 1941: 1935: 1929: 1922: 1912: 1901: 1890: 1885: 1880: 1879: 1878: 1874: 1864: 1859: 1855: 1851: 1840: 1837: 1833: 1829: 1823: 1819: 1814: 1801: 1792: 1789: 1788: 1787: 1783: 1779: 1763: 1759: 1748: 1741: 1736: 1731: 1727: 1716: 1709: 1704: 1701: 1695: 1691: 1686: 1679: 1673: 1669: 1664: 1657: 1649: 1643: 1639: 1634: 1631: 1628: 1616: 1610: 1606: 1601: 1598: 1594: 1590: 1584: 1580: 1575: 1570: 1566: 1561: 1560: 1559: 1557: 1551: 1547: 1538:Metric spaces 1537: 1535: 1529: 1524: 1519: 1517: 1513: 1509: 1501: 1494: 1486: 1484: 1474: 1471: 1467: 1451: 1445: 1442: 1439: 1427: 1424: 1416: 1409: 1405: 1398: 1392:Every net on 1391: 1384: 1380: 1378:for a proof). 1377: 1369: 1365: 1362: 1354: 1351: 1347: 1340: 1337: 1330: 1327: 1324:has a finite 1319: 1312: 1311: 1310: 1300: 1298: 1264: 1261: 1258: 1255: 1252: 1243: 1230: 1224: 1219: 1216: 1213: 1209: 1205: 1202: 1194: 1184: 1179: 1166: 1160: 1155: 1152: 1149: 1145: 1141: 1138: 1130: 1116: 1100: 1098: 1096: 1092: 1088: 1087:quasi-compact 1084: 1080: 1076: 1075:quasi-compact 1072: 1068: 1063: 1050: 1044: 1039: 1036: 1033: 1029: 1025: 1022: 1014: 1004: 999: 986: 980: 975: 972: 969: 965: 961: 958: 950: 936: 933: 925: 921: 914: 906: 904: 902: 897: 896:neighbourhood 893: 889: 885: 881: 877: 873: 872:bicompactness 869: 864: 862: 861:metric spaces 858: 854: 850: 846: 842: 838: 834: 830: 822: 820: 818: 813: 808: 798: 794: 790: 670: 666: 661:[0,1] 659: 658:unit interval 655: 647: 645: 643: 639: 635: 631: 630:Pavel Urysohn 627: 623: 619: 615: 611: 606: 604: 600: 596: 592: 591:Pierre Cousin 588: 584: 580: 576: 572: 568: 563: 561: 557: 553: 549: 545: 544:Hilbert space 541: 537: 533: 529: 528:David Hilbert 525: 520: 516: 512: 508: 507:Cesare Arzelà 504: 503:Giulio Ascoli 500: 495: 493: 489: 485: 481: 477: 473: 465: 463: 461: 457: 453: 448: 446: 442: 438: 437:Pavel Urysohn 434: 430: 426: 422: 418: 417:metric spaces 414: 410: 406: 402: 398: 394: 389: 369: 251: 250:unit interval 247: 243: 239: 235: 233: 227: 225: 221: 217: 213: 210: 208: 188: 165: 136: 132: 107: 103: 99: 98: 93: 89: 85: 81: 77: 73: 63: 56: 49: 44: 39: 30: 19: 18:Quasi-compact 5558:Publications 5423:Chern number 5413:Betti number 5317: 5296: / 5287:Key concepts 5235:Differential 5153: 5152: 5111: 5083: 5040: 5036: 5002: 4974: 4970: 4960: 4938: 4924: 4888:. New York: 4881: 4869: 4836: 4830: 4814: 4810: 4798: 4786: 4782: 4759: 4734: 4703: 4675: 4669: 4662:Borel, Émile 4654: 4647: 4628: 4604: 4595: 4591: 4576:Bibliography 4569:, p. 67 4562: 4550: 4538: 4526: 4514: 4502: 4495:Willard 1970 4490: 4478: 4466: 4454: 4442: 4430: 4418: 4405: 4394:. Retrieved 4390: 4380: 4359: 4347: 4331: 4320:. Retrieved 4315: 4294: 4288: 4277:. Retrieved 4270: 4261: 4241: 4237: 4233: 4216: := {0} 4213: 4207: 4200: 4196: 4178: 4168: 4160: 4156: 4144: 4140: 4136: 4130: 4011: 4007: 3979: 3975: 3947: 3943: 3939: 3933: 3905: 3838:Galois group 3827:Hilbert cube 3801:Stone spaces 3742: 3740:global field 3733:homeomorphic 3696: 3681:as spectrum. 3581:Banach space 3443: 3439: 3431: 3427: 3420: 3416: 3412: 3408: 3389: 3348: 3344: 3296: 3292: 3222: 3166: 3162: 3128: 3059:= 4, 5, ... 2945: 2942:= 3, 4, ... 2780: 2745: 2653: 2649:real numbers 2646: 2610: 2603:is compact. 2589: 2572: 2568: 2525: 2521: 2515: 2511: 2479: 2344: 2337: 2333: 2327: 2317: 2307: 2293: 2272: 2262: 2236: 2232: 2224: 2216: 2205: 2184: 2179: 2172:, since the 2163: 2150: 2146: 2142: 2137: 2079: 2075: 2073:. For each 2064: 2056: 2039: 2014: 1967: 1959: 1947: 1939: 1927: 1923: 1920: 1883: 1872: 1868: 1821: 1817: 1799: 1781: 1777: 1773: 1761: 1757: 1746: 1739: 1729: 1725: 1714: 1707: 1693: 1689: 1671: 1667: 1641: 1637: 1608: 1604: 1582: 1578: 1568: 1564: 1549: 1545: 1541: 1520: 1490: 1482: 1304: 1244: 1195: 1182: 1180: 1131: 1117:). That is, 1104: 1094: 1090: 1086: 1078: 1074: 1064: 1015: 1002: 1000: 951: 919: 911:Formally, a 910: 883: 871: 865: 826: 816: 809: 793:limit points 665:real numbers 654:finite space 651: 607: 571:Eduard Heine 564: 559: 496: 469: 451: 449: 420: 390: 232:sequentially 231: 228: 216:metric space 211: 206: 135:real numbers 96: 79: 69: 61: 54: 47: 5521:Wikiversity 5438:Key results 5144:1006.4131v1 4977:: 649–654. 4839:(1): 1–72. 4789:(5): 55–74. 4435:Kelley 1955 3713:such as an 3568:is compact. 3199:is compact. 2861:The closed 2803:is compact. 2710:is compact. 2615:is an open 2550:If a space 2443:is closed. 2270:to a point 1888:is compact. 1656:limit point 1573:is compact. 1408:ultrafilter 1181:there is a 1001:there is a 937:. That is, 849:subsequence 823:Definitions 593:(1895) and 583:Émile Borel 560:compactness 480:limit point 452:compact set 441:finite sets 421:compactness 242:subsequence 80:compactness 72:mathematics 5573:Categories 5367:CW complex 5308:Continuity 5298:Closed set 5257:cohomology 5160:PlanetMath 4807:Ascoli, G. 4801:: 142–159. 4694:26.0429.03 4423:Howes 1995 4396:2019-11-25 4352:Kline 1990 4336:Kline 1990 4322:2019-11-25 4279:2019-11-25 4254:References 4222:is all of 4149:and endow 4014:} ∪ 3982:} ∪ 3950:} ∪ 3803:, compact 3747:adele ring 3724:Since the 3211:Cantor set 3177:For every 2880:open cover 2812:singletons 2601:proper map 2592:continuous 2509:such that 2419:(assuming 2379:continuous 1858:singletons 1700:Cantor set 1530:or closed 1470:proper map 1318:open cover 1193:such that 1129:such that 1013:such that 949:such that 924:open cover 918:is called 220:equivalent 90:subset of 50:= (−∞, −2] 5546:geometric 5541:algebraic 5392:Cobordism 5328:Hausdorff 5323:connected 5240:Geometric 5230:Continuum 5220:Algebraic 5081:(1995) . 4935:(1990) . 4861:123251660 4635:EMS Press 4459:Mack 1967 4236:} : 4190:with the 3782:Hausdorff 3776:with the 3757:to allow 3751:John Tate 3640:ℓ 3532:− 3495:∈ 3174:inferred. 3016:π 2983:− 2978:π 2910:− 2693:empty set 2623:, by the 2581:-bounded. 2370:A finite 2133:given by 2116:→ 2101:: 2036:⊆ ... in 2011:⊇ ... in 1850:real line 1832:separable 1449:→ 1443:× 1359:with the 1262:⊂ 1256:⊂ 1217:∈ 1210:⋃ 1206:⊆ 1153:∈ 1146:⋃ 1142:⊆ 1105:A subset 1093:, plural 1091:compactum 1083:Hausdorff 1037:∈ 1030:⋃ 973:∈ 966:⋃ 922:if every 880:open sets 801:[0,∞) 567:continuum 450:The term 425:open sets 236:if every 222:in other 192:∞ 189:− 169:∞ 5594:Topology 5511:Wikibook 5489:Category 5377:Manifold 5345:Homotopy 5303:Interior 5294:Open set 5252:Homology 5201:Topology 5063:Archived 5001:(1996). 4916:1272666M 4908:31969970 4825:(1906). 4757:(1991). 4733:(1959). 4678:: 9–55. 4664:(1895). 4645:(1817). 4037:. Endow 3845:See also 3770:spectrum 3721:are not. 3573:spectrum 3437:for all 3396: → 3392: : 3225: : 3132:, cover 3122:, where 3086:The set 2856:Lindelöf 2682:Examples 2666:. Then 2590:Since a 2476:complete 2347:= (0, 1) 2308:A space 2182:)/ker ev 1836:Lindelöf 1615:sequence 1589:complete 1528:interval 1491:For any 1346:Lindelöf 1326:subcover 1095:compacta 1071:Bourbaki 935:subcover 845:sequence 789:boundary 554:who, in 403:and the 207:extended 102:interval 57:= (2, 4) 5536:general 5338:uniform 5318:compact 5269:Digital 5103:0507446 5059:1994440 5021:0205854 4991:0211382 4743:0124178 4211:. Then 4165:. Then 4087:. Then 3786:schemes 3772:of any 3575:of any 3442:,  3365:. Then 3361:or the 3189:-sphere 2846:In the 2545:regular 2482:closed. 2470:In any 2398:product 2042:, <) 2017:, <) 1970:, <) 1962:, <) 1950:, <) 1942:, <) 1930:, <) 1886:, <) 1875:, <) 1534:-ball. 1512:bounded 1079:compact 920:compact 894:– in a 892:locally 837:bounded 797:bounded 783:⁠ 771:⁠ 767:⁠ 755:⁠ 751:⁠ 739:⁠ 735:⁠ 723:⁠ 719:⁠ 707:⁠ 703:⁠ 691:⁠ 687:⁠ 675:⁠ 601:). The 445:locally 347:⁠ 335:⁠ 331:⁠ 319:⁠ 315:⁠ 303:⁠ 299:⁠ 287:⁠ 283:⁠ 271:⁠ 267:⁠ 255:⁠ 234:compact 88:bounded 5531:Topics 5333:metric 5208:Fields 5118:  5101:  5091:  5057:  5019:  5009:  4989:  4947:  4914:  4906:  4896:  4859:  4767:  4741:  4719:  4692:  4611:  4509:, §5.6 4226:, but 4159:, ∅, { 4005:, and 3836:(e.g. 3755:thesis 3700:tight. 3435:| 3406:| 3184:, the 2876:(0, 1) 2541:normal 2352:*(0,1) 2240:is a ( 2157:kernel 1802:> 0 1508:closed 1493:subset 1421:has a 1406:Every 1383:filter 1381:Every 1366:Every 1228:  1183:finite 1164:  1048:  1003:finite 984:  932:finite 930:has a 876:covers 833:closed 817:within 427:that " 399:. The 353:(0, 1) 84:closed 5313:Space 5139:arXiv 5066:(PDF) 5055:JSTOR 5033:(PDF) 4857:S2CID 4674:. 3. 4232:{{0, 3925:Notes 3697:tight 3579:on a 3115:− 1, 2674:is a 2658:be a 2411:In a 2372:union 2289:monad 2168:is a 1752:⊆ ... 1720:⊇ ... 1521:As a 1468:(see 1464:is a 882:(see 812:disks 785:, ... 458:of a 429:cover 349:, ... 212:would 5116:ISBN 5089:ISBN 5007:ISBN 4945:ISBN 4904:OCLC 4894:ISBN 4765:ISBN 4717:ISBN 4609:ISBN 4206:0 ∈ 4182:Let 4134:Let 4121:and 4091:and 4083:and 4079:are 4071:and 4067:are 3937:Let 3825:The 3814:The 3768:The 3738:Any 3731:are 3571:The 3209:The 3119:+ 1) 2937:for 2787:The 2713:Any 2687:Any 2654:Let 2543:and 2519:and 2501:and 2489:and 2396:The 2145:) = 2057:Let 1834:and 1591:and 1510:and 1376:nets 1348:and 1085:and 855:and 835:and 652:Any 628:and 599:1904 587:1895 556:1906 530:and 505:and 476:1817 435:and 411:and 181:and 86:and 5158:on 5045:doi 5041:124 4979:doi 4849:hdl 4841:doi 4709:doi 4690:JFM 4680:doi 4411:set 4139:= { 4010:= { 3978:= { 3942:= { 3753:'s 3488:sup 3286:in 3167:not 2817:In 2806:No 2791:or 2505:in 2485:If 2480:not 2461:If 2446:If 2387:If 2300:). 2291:of 2279:of 2266:is 2221:in 2198:is 2159:of 1826:is 1754:in 1722:in 1676:is 1658:in 1646:is 1617:in 1587:is 1558:): 1498:of 1410:on 1385:on 1370:on 1368:net 1344:is 1320:of 1305:If 926:of 673:1, 663:of 70:In 5575:: 5099:MR 5097:. 5077:; 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Index

Quasi-compact
Compactness (disambiguation)

Heine–Borel theorem
mathematics
general topology
closed
bounded
Euclidean space
limiting values
interval
rational numbers
irrational numbers
real numbers
extended real number line
metric space
equivalent
topological spaces
sequentially compact
infinite sequence
subsequence
Bolzano–Weierstrass theorem
unit interval
Maurice Fréchet
spaces of functions
Arzelà–Ascoli theorem
Peano existence theorem
sequential compactness
limit point compactness
metric spaces

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