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Continuum theory, point-set topology, spaces with algebraic structure, foundations, dimension theory, local and global properties.

1 vote
0 answers
83 views

Topologies on spaces of linear sections

Let $X$ and $Y$ be topological linear spaces which are complete & Hausdorff, and admit dual spaces which separate points. Suppose the topologies are non-separable and non-metrizable. Let $f : X \to Y …
Tom LaGatta's user avatar
  • 8,532
3 votes
2 answers
437 views

What is a good example of a hyperspace where the base space is non-Hausdorff?

Let $X$ be a topological space, and let $\operatorname{CL}(X)$ be its hyperspace. That is, $\operatorname{CL}(X)$ is the set of closed subsets of $X$, equipped with the minimal topology so that the ca …
Tom LaGatta's user avatar
  • 8,532
5 votes
1 answer
399 views

Example: a locally convex TVS which is not compactly generated

Is there an example of a locally convex topological vector space which is not compactly generated? (any such example must be non-Fréchet, since all Fréchet spaces are compactly generated) (note: I a …
Tom LaGatta's user avatar
  • 8,532
9 votes
1 answer
780 views

Topological Generalization of Whitney's Extension Theorem

From Wikipedia: In mathematics, in particular in mathematical analysis, the Whitney extension theorem is a partial converse to Taylor's theorem. Roughly speaking, the theorem asserts that if $A$ i …
Tom LaGatta's user avatar
  • 8,532
1 vote
0 answers
654 views

Extending a homeomorphism from a dense set [closed]

Let $X$ and $Y$ be Hausdorff topological spaces, and let $f : X \to Y$ be a Borel-measurable function. Suppose that $D \subseteq X$ is dense, that the image $f(D) \subseteq Y$ is dense, and that $f$ i …
Tom LaGatta's user avatar
  • 8,532
5 votes
1 answer
2k views

Dual of the space of continuous functions

Let $T \subseteq \mathbb R$ be a closed set of real numbers. Let $X := C(T, \mathbb R)$ denote the Fréchet space of continuous real-valued functions on $T$. The topology on $X$ is generated by seminor …
Tom LaGatta's user avatar
  • 8,532
4 votes
1 answer
472 views

Isomorphisms between topological vector spaces [closed]

Let $f : X \to Y$ be a continuous map of complete topological vector spaces. Suppose that $A \subseteq X$ and $B \subseteq Y$ are proper, dense linear subspaces, and that the restriction map $f : A \t …
Tom LaGatta's user avatar
  • 8,532
3 votes
0 answers
176 views

Extending a Hilbert space isometrically

Let $H$ be a Hilbert space, and let $X$ be a topological vector space. Under what conditions on the topologies of $X$ and $H$ does there exist an injective, continuous linear map $f : H \to X$? Su …
Tom LaGatta's user avatar
  • 8,532
2 votes
1 answer
381 views

Properties of the weak-$*$ topology

Let $X$ be a topological affine space over a complete base field $\mathbb S := \mathbb C$, $\mathbb R$ or $\mathbb Q_p$. Let $X^*$ be the dual space of continuous affine functionals equipped with the …
5 votes
1 answer
399 views

Is every bornological space measurable?

Every topological space is measurable, since we may canonically equip a topological space with its Borel $\sigma$-algebra. A bornological space is like a topological space, except the structure descri …
Tom LaGatta's user avatar
  • 8,532
3 votes
1 answer
958 views

When is the support of a Radon measure separable?

Let $X$ be a topological space, equipped with its Borel $\sigma$-algebra $\mathcal B(X)$, and let $\mathbb P$ be a Radon probability measure on $(X, \mathcal B(X))$. Recall that the support of the mea …
Tom LaGatta's user avatar
  • 8,532
6 votes
2 answers
994 views

On the uncountability of zero sets

If $f$ is any real-valued function, we define its zero set $Z_f = \{ x : f(x) = 0 \}$. Obviously, the zero set of a nice function can be uncountable. e.g., if $f(x) = 0$ on an uncountable domain. I …
Tom LaGatta's user avatar
  • 8,532
1 vote
1 answer
350 views

Agreement of two topologies on a linear space

I'm dealing with the formalism of an abstract Wiener space, and I'm not sure if two relevant topologies coincide. Let $X$ be a topological vector space, and let $X^*$ be its dual space of continuous …
Tom LaGatta's user avatar
  • 8,532
6 votes
1 answer
391 views

Does a metric refine the weak-* topology on a dual space?

Let $X$ be a topological affine space over $\mathbb C$, with no additional assumptions. Let $X^*$ denote its dual space of continuous affine functionals $X \to \mathbb C$, equipped with the weak-$*$ t …
Tom LaGatta's user avatar
  • 8,532
2 votes
1 answer
547 views

Is this a closed set?

Let $\Theta$ and $X$ be two (Hausdorff) topological spaces. Let $\mathbb P : \Theta \to \Delta(X)$ be a "statistical model", i.e., a continuous function from parameter space $\Theta$ to the space of p …
Tom LaGatta's user avatar
  • 8,532

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