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Topological space whose topology has a countable base
In topology, a second-countable space, also called a completely separable space, is a topological space whose topology has a countable base. More explicitly
Second-countable_space
Topological space where each point has a countable neighbourhood basis
mathematics, a first-countable space is a topological space satisfying the "first axiom of countability". Specifically, a space X {\displaystyle X} is
First-countable_space
Topological space with a dense countable subset
In mathematics, a topological space is called separable if it contains a countable dense subset; that is, there exists a sequence ( x n ) n = 1 ∞ {\displaystyle
Separable_space
Topological concept
Lindelöf space, in particular in a second-countable space, is countable. This is proved by a similar argument as in the result above for compact spaces. A collection
Locally_finite_collection
Index of articles associated with the same name
set first-countable space: every point has a countable neighbourhood basis (local base) second-countable space: the topology has a countable base separable
Axiom_of_countability
Topological space which is a generalization of certain compact spaces
Hausdorff second-countable space is paracompact. The Sorgenfrey line is paracompact, even though it is neither compact, locally compact, second countable, nor
Paracompact_space
Mathematical concept
measure of the entire sample space is equal to one: P ( Ω ) = 1 {\displaystyle P(\Omega )=1} . For a countable sample space Ω {\displaystyle \Omega } ,
Probability_space
Type of topological space
particular, every countable space is Lindelöf. A Lindelöf space is compact if and only if it is countably compact. Every second-countable space is Lindelöf
Lindelöf_space
Curve whose range contains the unit square
theorem, second-countable then implies metrizable. Conversely, a compact metric space is second-countable. There are many natural examples of space-filling
Space-filling_curve
Concept in mathematics
Lindelöf. Every second-countable space (it has a countable base of open sets) is a separable space (it has a countable dense subset). A metric space is separable
Axiom_of_countable_choice
topological space is called countably compact if every countable open cover has a finite subcover. A topological space X is called countably compact if
Countably_compact_space
Topological space characterized by sequences
very weak axiom of countability, and all first-countable spaces (notably metric spaces) are sequential. In any topological space ( X , τ ) , {\displaystyle
Sequential_space
Type of topological space
Every regular second-countable space is completely normal, and every regular Lindelöf space is normal. Also, all fully normal spaces are normal (even
Normal_space
Concept in set theory
confused with the countable ordinal obtained by ordinal exponentiation). The Baire space is defined to be the Cartesian product of countably infinitely many
Baire_space_(set_theory)
Collection of open sets used to define a topology
spaces are necessarily second countable); as well as the fact that compact Hausdorff spaces are metrizable exactly in case they are second countable.
Base_(topology)
Branch of topology
set first-countable space: every point has a countable neighbourhood basis (local base) second-countable space: the topology has a countable base separable
General_topology
Topological space that is homeomorphic to a metric space
This states that every Hausdorff second-countable regular space is metrizable. So, for example, every second-countable manifold is metrizable. (Historical
Metrizable_space
Type of topological space
first-countable space is a Fréchet–Urysohn space. Consequently, every second-countable space, every metrizable space, and every pseudometrizable space is
Fréchet–Urysohn_space
fact above about second countable scattered spaces, together with the fact that a subset of a second countable space is second countable.) Furthermore,
Scattered_space
Type of topological space
metric space is bounded. Every discrete space is first-countable; it is moreover second-countable if and only if it is countable. Every discrete space is
Discrete_space
Concept in topology
Polish space is a separable completely metrizable topological space; that is, a space homeomorphic to a complete metric space that has a countable dense
Polish_space
directed joins. Second category See Meagre. Second-countable A space is second-countable or perfectly separable if it has a countable base for its topology
Glossary_of_general_topology
Property of topological space
a Gδ space is a Gδ space. Every metrizable space is a Gδ space. The same holds for pseudometrizable spaces. Every second countable regular space is a
Gδ_space
Type of topological space
mathematics, a topological space is said to be σ-compact if it is the union of countably many compact subspaces. A space is said to be σ-locally compact
Σ-compact_space
List of concrete topologies and topological spaces
countable. Cofinite topology Double-pointed cofinite topology Ordinal number topology Pseudo-arc Ran space Tychonoff plank Discrete two-point space −
List_of_topologies
Generalization of mass, length, area and volume
{\displaystyle E\in \Sigma ,\ \ \mu (E)\geq 0} Countable additivity (or σ-additivity): For all countable collections { E k } k = 1 ∞ {\displaystyle
Measure_(mathematics)
Locally convex topological vector space that is also a complete metric space
translation-invariant metric, the second a countable family of seminorms. A topological vector space X {\displaystyle X} is a Fréchet space if and only if it satisfies
Fréchet_space
Paracompact space Locally compact space Compactly generated space Axiom of countability Sequential space First-countable space Second-countable space Separable
List of general topology topics
List_of_general_topology_topics
Mathematical set that can be enumerated
is countable if either it is finite or it can be made in one to one correspondence with the set of natural numbers. Equivalently, a set is countable if
Countable_set
Type of topological space
Euclidean space. For any manifold the properties of being second-countable, Lindelöf, and σ-compact are all equivalent. Every second-countable manifold
Topological_manifold
Mathematical property of a space
countable local base. Second-countable. A space is second-countable if it has a countable base for its topology. Second-countable spaces are always separable
Topological_property
Normed vector space that is complete
Banach space cannot be the union of countably many closed subspaces, unless it is already equal to one of them; a Banach space with a countable Hamel basis
Banach_space
Type of vector space in math
is countably infinite, it allows identifying the Hilbert space with the space of the infinite sequences that are square-summable. The latter space is
Hilbert_space
Type of mathematical space
is second-countable, separable and Lindelöf – these three conditions are equivalent for metric spaces. The converse is not true; e.g., a countable discrete
Compact_space
Smallest ordinal number that, considered as a set, is uncountable
) {\displaystyle [0,\omega _{1})} is first-countable, but neither separable nor second-countable. The space [ 0 , ω 1 ] = ω 1 + 1 {\displaystyle [0,\omega
First_uncountable_ordinal
Vector space on which a distance is defined
space C ∞ ( K ) , {\displaystyle C^{\infty }(K),} as defined in the article on spaces of test functions and distributions, is defined by a countable family
Normed_vector_space
Algebraic structure in linear algebra
are countably infinite-dimensional vector spaces, and many function spaces have the cardinality of the continuum as a dimension. Many vector spaces that
Vector_space
vector space (TVS) is said to be countably barrelled if every weakly bounded countable union of equicontinuous subsets of its continuous dual space is again
Countably_barrelled_space
Algebraic structure of set algebra
complement, countable unions, and countable intersections. The ordered pair ( X , Σ ) {\displaystyle (X,\Sigma )} is called a measurable space. The set X
Σ-algebra
countable union of open intervals. Lindelöf's lemma is also known as the statement that every open cover in a second-countable space has a countable subcover
Lindelöf's_lemma
Vector space with generalized dot product
product space is a normed vector space. If this normed space is also complete (that is, a Banach space) then the inner product space is a Hilbert space. If
Inner_product_space
Concept in topology
In mathematics, a topological space X {\displaystyle X} is said to be a Baire space if countable unions of closed sets with empty interior also have empty
Baire_space
Book by Lynn Steen
the literature. For instance, an example of a first-countable space which is not second-countable is counterexample #3, the discrete topology on an uncountable
Counterexamples_in_Topology
Certain topology in mathematics
of the limit of the sequence, if it has one. The space ω1 is first-countable but not second-countable, and ω1+1 has neither of these two properties, despite
Order_topology
Mathematical space with a notion of distance
original topological space (a disjoint union of countably many intervals) lead to different topologies on the quotient. A topological space is sequential if
Metric_space
"Small" subset of a topological space
set or a set of first category) is a subset of a topological space that is a countable union of subsets that are not dense in any non-empty open set
Meagre_set
Generalization of "n-th" to infinite cases
first uncountable cardinality. Cantor's second theorem becomes: If P′ is countable, then there is a countable ordinal α such that P(α) = ∅. Its proof
Ordinal_number
space (TVS) is said to be countably quasi-barrelled if every strongly bounded countable union of equicontinuous subsets of its continuous dual space is
Countably quasi-barrelled space
Countably_quasi-barrelled_space
Natural number
called an involution. Two is most commonly a determiner used with plural countable nouns, as in two days or I'll take these two. Two is a noun when it refers
2
Random process independent of past history
having discrete time in either countable or continuous state space (thus regardless of the state space). The system's state space and time parameter index need
Markov_chain
Mathematical set with some added structure
analytic space Drinfeld's symmetric space Eilenberg–Mac Lane space Euclidean space Fiber space Finsler space First-countable space Fréchet space Function
Space_(mathematics)
Class of mathematical sets
topological space X {\displaystyle X} that contains both the empty set and the entire set X {\displaystyle X} , and is closed under countable union and
Borel_set
Set of all possible outcomes or results of a statistical trial or experiment
or symbols. They can also be finite, countably infinite, or uncountably infinite. A subset of the sample space is an event, denoted by E {\displaystyle
Sample_space
Branch of mathematical logic
express the principle "Every countable vector space has a basis" but it cannot express the principle "Every vector space has a basis". In practical terms
Reverse_mathematics
Line formed by the real numbers
that the topological space supports.) The real line is a locally compact space and a paracompact space, as well as second-countable and normal. It is also
Number_line
Function spaces generalizing finite-dimensional p norm spaces
-norm defined above. If I {\displaystyle I} is countably infinite, this is exactly the sequence space ℓ p {\displaystyle \ell ^{p}} defined above. For
Lp_space
Topological space with a notion of uniform properties
necessarily a metric if the space is Hausdorff. In particular, if the topology of a vector space is Hausdorff and definable by a countable family of seminorms
Uniform_space
Topological space that is maximally disconnected
to a subset of a countable product of discrete spaces. It is in general not true that every open set in a totally disconnected space is also closed. It
Totally_disconnected_space
Space with topology generated by convex sets
separated, and countable, and the space is complete, so this metrizable space is a Fréchet space. It is known as the Schwartz space, or the space of functions
Locally convex topological vector space
Locally_convex_topological_vector_space
Topological space in mathematics
any countable ordinal α {\displaystyle \alpha } , pasting together α {\displaystyle \alpha } copies of [ 0 , 1 ) {\displaystyle [0,1)} gives a space which
Long_line_(topology)
In mathematics, vector space of linear forms
\mathbb {R} ^{\infty }} is countably infinite, whereas R N {\displaystyle \mathbb {R} ^{\mathbb {N} }} does not have a countable basis. This observation
Dual_space
Topological space that is connected
simply connected after removal of countably many points. Any topological vector space, e.g. any Hilbert space or Banach space, over a connected field (such
Connected_space
Vector space of infinite sequences
{\displaystyle H} be a separable Hilbert space. Every orthogonal set in H {\displaystyle H} is at most countable (i.e. has finite dimension or ℵ 0 {\displaystyle
Sequence_space
or T3, and some authors allow a countable or even arbitrary number of isolated points. The existence of a Luzin space is independent of the axioms of
Luzin_space
Topological vector space whose topology can be defined by a metric
but at most countably many of these TVSs have the trivial topology. Every complete pseudometrizable TVS is a barrelled space and a Baire space (and thus
Metrizable topological vector space
Metrizable_topological_vector_space
Proof in set theory
that: The set T is uncountable. The proof starts by assuming that T is countable. Then all its elements can be written in an enumeration s1, s2, ... ,
Cantor's_diagonal_argument
Topological space
number of points. It is Hausdorff regular normal It is not: second-countable first-countable metrizable compact sequential Fréchet–Urysohn There is no sequence
Arens–Fort_space
Infinite cardinal number
(this follows from the fact that the union of a countable number of countable sets is itself countable). This fact is analogous to the situation in ℵ 0
Aleph_number
Generalization of the notion of convergence that is found in general topology
In mathematics, a convergence space, also called a generalized convergence, is a set together with a relation called a convergence that satisfies certain
Convergence_space
Generalization of boundedness
uniformly bounded. In words, given any countable family of bounded sets in a metrizable locally convex space, it is possible to scale each set by its
Bounded set (topological vector space)
Bounded_set_(topological_vector_space)
Mathematical function revertible near each point
between two Hausdorff second-countable spaces where X {\displaystyle X} is a Baire space and Y {\displaystyle Y} is a normal space. If every fiber of f
Local_homeomorphism
Functional analysis concept
_{n}\to 0} . When the Hilbert space is in addition separable, one can mix the basis ( e n ) {\displaystyle (e_{n})} with a countable orthonormal basis for the
Compact operator on Hilbert space
Compact_operator_on_Hilbert_space
Mathematical concept
also second-countable (there are only finitely many open sets) and separable (since the space itself is countable). If a finite topological space is T1
Finite_topological_space
Axiom of set theory
vector space with no basis. There is a vector space with two bases of different cardinalities. There is a free complete Boolean algebra on countably many
Axiom_of_choice
can be separated by neighbourhoods. (X is a regular Hausdorff space.) There is a countable collection of open covers of X, such that for any closed set
Moore_space_(topology)
II. It is normal Haudsdorff, compact, separable, and first-countable but not second-countable. Steen, L. A.; Seebach, J. A. (1995), Counterexamples in Topology
Helly_space
Bounded sequence in finite-dimensional Euclidean space has a convergent subsequence
index set) has a convergent subsequence if and only if there exists a countable set K ⊆ I {\displaystyle K\subseteq I} such that ( x m ) m ∈ K {\displaystyle
Bolzano–Weierstrass_theorem
Broadest definition of sizes in integer-dimensional spaces
a way that is compatible with countable unions and other kinds of countable limits of sets. For example, every countable subset of the real line has Lebesgue
Lebesgue_measure
On topological spaces where the intersection of countably many dense open sets is dense
sufficient conditions for a topological space to be a Baire space (a topological space such that the intersection of countably many dense open sets is still dense)
Baire_category_theorem
Geometric theorem
years earlier: the surface of a unit sphere in space is a disjoint union of three sets B, C, D and a countable set E such that, on the one hand, B, C, D are
Banach–Tarski_paradox
Vector space with a notion of nearness
Fréchet spaces: these are complete locally convex spaces where the topology comes from a translation-invariant metric, or equivalently: from a countable family
Topological_vector_space
Topological vector spaces
) {\displaystyle C^{\infty }(U)} can be obtained by taking a suitable countable Fréchet combination of any one of the above defining families of seminorms
Spaces of test functions and distributions
Spaces_of_test_functions_and_distributions
Generalization of compactness
for every neighborhood U {\displaystyle U} of the identity and every countably infinite subset I {\displaystyle I} of S , {\displaystyle S,} there exist
Totally_bounded_space
Analog of Fubini's theorem for arbitrary second countable Baire spaces
theorem for arbitrary second countable Baire spaces. Let X and Y be second countable Baire spaces (or, in particular, Polish spaces), and let A ⊂ X × Y
Kuratowski–Ulam_theorem
Topological vector space
mathematics, an LF-space, also written (LF)-space, is a topological vector space (TVS) X that is a locally convex inductive limit of a countable inductive system
LF-space
Generalization of finite-dimensional Euclidean spaces different from Hilbert spaces
condition that the space should also be a Fréchet space. (This means that the space is complete and the topology is given by a countable family of seminorms
Nuclear_space
Theorem in economics
contour sets are topologically closed; The space X is second-countable. This means that there is a countable set S of open sets, such that every open set
Utility representation theorem
Utility_representation_theorem
Area of mathematical logic
characterised by properties of their type space: For a complete first-order theory T in a finite or countable signature the following conditions are equivalent:
Model_theory
Countable intersection of open sets
mathematical field of topology, a Gδ set is a subset of a topological space that is a countable intersection of open sets. The notation originated from the German
Gδ_set
Topology on the real numbers
Hausdorff space. In terms of countability axioms, R l {\displaystyle \mathbb {R} _{l}} is first-countable and separable, but not second-countable. In terms
Lower_limit_topology
Set of points on a line segment with certain topological properties
naturally homeomorphic to the countable product 2 _ N {\displaystyle {\underline {2}}^{\mathbb {N} }} of the discrete two-point space 2 _ {\displaystyle {\underline
Cantor_set
Two-dimensional manifold
explicitly or implicitly, that as a topological space a surface is also nonempty, second-countable, and Hausdorff. It is also often assumed that the
Surface_(topology)
Topology where a set is open if it contains a particular point
Sierpiński space. If X is finite (with at least 3 points), the topology on X is called the finite particular point topology. If X is countably infinite
Particular_point_topology
Topological space
that a subspace of a separable space need not be separable. The Moore plane is first countable, but not second countable or Lindelöf. The Moore plane is
Moore_plane
Way of decomposing a topological space
{\displaystyle V} is a topological space (often we require that it is locally compact, Hausdorff, and second countable), S {\displaystyle {\mathcal {S}}}
Thom–Mather_stratified_space
Rule in mathematics
{\displaystyle C(X)} has countable fan tightness. Compact space Sigma-compact Menger space Hurewicz space Rothberger space Menger, Karl (1924). "Einige
Selection_principle
In functional analysis, a Hilbert space
Hilbert space (RKHS) is a Hilbert space of functions in which point evaluation is a continuous linear functional. Specifically, a Hilbert space H {\displaystyle
Reproducing kernel Hilbert space
Reproducing_kernel_Hilbert_space
Everything in space and time
responded to these paradoxes by developing the notion of a potential countable infinity, as well as the infinitely divisible continuum. The Indian philosopher
Universe
Basic object in measure theory; set and a sigma-algebra
\left(X,{\mathcal {F}}_{2}\right).} If X {\displaystyle X} is finite or countably infinite, the σ {\displaystyle \sigma } -algebra is most often the power
Measurable_space
K_{i+1}} , meaning the space is σ-compact (i.e., a countable union of compact subsets.) If there is an exhaustion by compact sets, the space is necessarily locally
Exhaustion_by_compact_sets
SECOND COUNTABLE-SPACE
SECOND COUNTABLE-SPACE
Girl/Female
Indian
Second
Surname or Lastname
English
English : from an Old English personal name composed of the elements ēast ‘grace’, ‘beauty’ + mund ‘protection’. This name was also used by the Norman, among whom it represents a continental Germanic cognate of the Old English name.
Female
English
From the name of the state of Arizona in the United States of America, a place considered sacred by the Native Americans. It was named after Sedona Miller Schnebly (1877-1950), the wife of the city's first postmaster. Meaning unknown.
Boy/Male
Assamese, Celebrity, Gujarati, Hindu, Indian, Jain, Kannada, Malayalam, Marathi, Oriya, Punjabi, Sanskrit, Sikh, Tamil, Telugu, Traditional
Sky; Lord of Day; Uncountable; Space
Girl/Female
Spanish
Lively.
Boy/Male
Hindu, Indian
Un Countable; Multiple; Countless
Boy/Male
Hindu, Indian
Uncountable
Surname or Lastname
English
English : from Richward, a Norman personal name composed of the Germanic elements rīc ‘power(ful)’ + ward ‘guard’.French : from Old French record, recort ‘recollection’, ‘account’, ‘testimony’, and by extension ‘witness’, hence perhaps a nickname for someone who had given evidence in a court of law, or a metonymic occupational name for a clerk who recorded court proceedings.New England variant of French Ricard, reflecting an Americanized spelling of the Canadian pronunciation.
Girl/Female
Tamil
Second
Male
English
Variant spelling of Middle English Estmond, ESMOND means "gracious protector."Â
Surname or Lastname
English
English : occupational name for the law-enforcement officer of a parish, from Middle English, Old French conestable, cunestable, from Late Latin comes stabuli ‘officer of the stable’. The title was also borne by various other officials during the Middle Ages, including the chief officer of the household (and army) of a medieval ruler, and this may in some cases be the source of the surname.Americanized spelling of Dutch Constapel, an occupational name for the chief gunner aboard a ship or in the garrison of a fort.
Boy/Male
Hindu, Indian
Uncountable
Boy/Male
English
Protected by God. Grace and protection. From the Old English name Estmund. Commonly used as a...
Boy/Male
Norse
Pointable.
Female
English
Anglicized form of Scottish Gaelic Seònaid, SEONA means "God is gracious."
Boy/Male
Indian
Second
Boy/Male
Christian & English(British/American/Australian)
Protective Grace
Girl/Female
Biblical
Second.
Boy/Male
African American American
Of man.
Boy/Male
American, British, Christian, English, French, German
Wealthy Protector; Protected by Grace; Gracious Protector
SECOND COUNTABLE-SPACE
SECOND COUNTABLE-SPACE
Boy/Male
Tamil
White
Boy/Male
Arabic, Muslim
Life of the World
Girl/Female
Tamil
Giver of Joy, Delighted
Girl/Female
Australian, Greek
Flower of Glory
Surname or Lastname
English
English : habitational name from Oughtibridge, South Yorkshire, which is probably named from an unattested Old English female personal name, Ūhtgifu + Old English brycg ‘bridge’.
Girl/Female
Indian, Punjabi, Sikh
The Brave Soldier
Boy/Male
African
God protects'.
Boy/Male
Hebrew
Ploughman. Son of Talmai (Talmai is a, meaning abounding in furrows.) Famous bearer: St...
Male
German
Frisian pet form of German Anton, possibly TÖNJES means "invaluable."Â
Female
English
English name derived from the season name, "winter." The word may derive from Proto-Indo-European *wind-, WINTER means "white."
SECOND COUNTABLE-SPACE
SECOND COUNTABLE-SPACE
SECOND COUNTABLE-SPACE
SECOND COUNTABLE-SPACE
SECOND COUNTABLE-SPACE
a.
See Accountable.
a.
Having the power of second-sight.
adv.
In the second place.
a.
Of the rank or degree below the best highest; inferior; second-rate; as, a second-class house; a second-class passage.
n.
A unit for the measurement of small intervals of time, such that 1012 (ten trillion) of these units make one second.
imp. & p. p.
of Second
a.
The sixtieth part of a minute of time or of a minute of space, that is, the second regular subdivision of the degree; as, sound moves about 1,140 English feet in a second; five minutes and ten seconds north of this place.
n.
The quality or state of being accountable; accountability.
n.
The second part in a concerted piece.
adv.
Secondly; in the second place.
a.
Accountable.
n.
One who seconds or supports what another attempts, affirms, moves, or proposes; as, the seconder of an enterprise or of a motion.
prep.
Past, out of the reach or sphere of; further than; greater than; as, the patient was beyond medical aid; beyond one's strength.
a.
To follow or attend for the purpose of assisting; to support; to back; to act as the second of; to assist; to forward; to encourage.
a.
Of the second size, rank, quality, or value; as, a second-rate ship; second-rate cloth; a second-rate champion.
a.
Capable of being numbered.
a.
Cutting; divivding into two parts; as, a secant line.
n.
The second part in a concerted piece; -- often popularly applied to the alto.
a.
Liable to be called on to render an account; answerable; as, every man is accountable to God for his conduct.
a.
Being of the same kind as another that has preceded; another, like a protype; as, a second Cato; a second Troy; a second deluge.