Not to be confused with Separated space or Separation axiom.
In mathematics, a topological space is called separable if it contains a countable, dense subset; that is, there exists a sequence of elements of the space such that every nonempty open subset of the space contains at least one element of the sequence.
Like the other axioms of countability, separability is a "limitation on size", not necessarily in terms of cardinality (though, in the presence of the Hausdorff axiom, this does turn out to be the case; see below) but in a more subtle topological sense. In particular, every continuous function on a separable space whose image is a subset of a Hausdorff space is determined by its values on the countable dense subset.
Contrast separability with the related notion of second countability, which is in general stronger but equivalent on the class of metrizable spaces.
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...
of space. From this perspective, the natural state space of a boson might seem to be a non-separablespace. However, it is only a small separable subspace...
of a separable Banach space need not be separable, but: Theorem — Let X {\displaystyle X} be a normed space. If X ′ {\displaystyle X'} is separable, then...
roots is equal to its degree Separable sigma algebra, a separablespace in measure theory Separablespace, a topological space that contains a countable...
topology, a Polish space is a separable completely metrizable topological space; that is, a space homeomorphic to a complete metric space that has a countable...
Hausdorff space is metrizable if and only if it is second-countable. Urysohn's Theorem can be restated as: A topological space is separable and metrizable...
mathematics, S-space is a regular topological space that is hereditarily separable but is not a Lindelöf space. L-space is a regular topological space that is...
in an n-dimensional Euclidean space. Then X 0 {\displaystyle X_{0}} and X 1 {\displaystyle X_{1}} are linearly separable if there exist n + 1 real numbers...
construction of Tsirelson space in 1974. The dual statement, that every separable Banach space is linearly isometric to a quotient space of ℓ1, was answered...
In quantum mechanics, separable states are multipartite quantum states that can be written as a convex combination of product states. Product states are...
p}(\Omega )} is a Banach space. For p < ∞ , W k , p ( Ω ) {\displaystyle p<\infty ,W^{k,p}(\Omega )} is also a separablespace. It is conventional to denote...
topology, a cosmic space is any topological space that is a continuous image of some separable metric space. Equivalently (for regular T1 spaces but not in general)...
space is Polish if it is separable and completely metrizable, i.e. if it is homeomorphic to a separable and complete metric space. Polyadic A space is...
subset of this space, and this is a non-separable subset of the separablespace S {\displaystyle \mathbb {S} } . It shows that separability does not inherit...
Any separable inner product space has an orthonormal basis. Using the Hausdorff maximal principle and the fact that in a complete inner product space orthogonal...
second-countable space is first countable, separable, and Lindelöf. Every σ-compact space is Lindelöf. Every metric space is first countable. For metric spaces, second-countability...
Marczewski proved that the topological dimension, for arbitrary metrisable separablespace X, coincides with the Hausdorff dimension under one of the metrics...
a separable extension if for every α ∈ E {\displaystyle \alpha \in E} , the minimal polynomial of α {\displaystyle \alpha } over F is a separable polynomial...
separable spaces is a separablespace and, thus, ccc. A metric space is ccc if and only if it's separable. In general, a ccc topological space need not...
separated if it is Hausdorff; importantly, "separated" does not mean separable. The topological and linear algebraic structures can be tied together...
on separablespaces and most applications to other areas of mathematics or physics only use separable Hilbert spaces. Note that if the measure spaces (X...
Arzelà–Ascoli theorem. A metric space is separable if and only if it is homeomorphic to a totally bounded metric space. The closure of a totally bounded...
For a stochastic process to be separable, in addition to other conditions, its index set must be a separablespace, which means that the index set has...