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Banach spaces, function spaces, real functions, integral transforms, theory of distributions, measure theory.

9 votes
Accepted

Is any dual metrizable locally convex space a Frechet space?

I am not 100% clear what you are asking, but I will answer according to two interpretations: a) Suppose that $F$, a metrizable TVS, is the strong dual of $E$, a locally convex TVS. Need $F$ be comple …
Robert Furber's user avatar
4 votes
Accepted

Sequential Continuity in dual spaces of separable Banach Spaces

This is true. To show it, in the following I will use $\langle \mbox{-}, \mbox{-} \rangle$ for the pairing between a space and its dual (with the vectors from the space on the left, the dual on the ri …
Robert Furber's user avatar
3 votes

Complete dual of bornological space

Jochen is quite right. I have another example, just using any irreflexive Banach space $A$. The space $E = (A^*,\mu(A^*,A))$ is Mackey, by definition. The bounded sets in $E$ are the same as the norm- …
Robert Furber's user avatar
3 votes
Accepted

Convergence in $\sigma(\mathcal{E}',\mathcal{E})$ versus $\beta(\mathcal{E}',\mathcal{E})$

The answer is yes. First, since $\newcommand{E}{\mathcal{E}}\E$ is a Fréchet space, it is barrelled, and so any $\sigma(\E',\E)$-bounded subset of $\E'$ is equicontinuous, and therefore bounded in any …
Robert Furber's user avatar
14 votes

A topological vector space $X$ is separable if its dual space $X^*$ is separable?

YCor has given a counterexample for topological vector spaces. The statement is still false for locally convex spaces. Consider the space $X$ defined to be a locally convex coproduct of $\newcommand{\ …
Robert Furber's user avatar
5 votes

Set of w*-continuous operators closed for the weak* topology or not?

The answer is no. I know that for some people here, saying "It's false for $X = \ell^1$" would be a good enough hint, but I also know that this question originated on Math StackExchange, so I've inclu …
Robert Furber's user avatar
12 votes
Accepted

Unconditionally convergent series in some functional spaces

A good resource for these things is Section IV.10 of Schaefer's Topological Vector Spaces, so you should look there for the proofs of the following statements. For $E$ a locally convex space, let $\el …
Robert Furber's user avatar
3 votes
Accepted

Conditions under which a linear functional on a space of measures must be integration of a f...

If you work in terms of topologies on M, then the way to go is to use the theory of dualities from functional analysis. The basic theory of these things can be found in books called "Topological Vecto …
Robert Furber's user avatar
5 votes

Duality between Banach spaces and compact convex spaces

Judging by what you say in the question, I think you are referring to what Świrszcz called "Saks spaces" in this article: Monadic functors and convexity, Bull. Acad. Polon. Sci. Ser. Sci. Math. Astro …
Robert Furber's user avatar
9 votes

A characterization of $L_1(\mu)$ in $L_\infty(\mu)^*$

The criterion suggested in the question works fine for $\sigma$-finite spaces, and Michael Greinecker's answer is correct under this assumption. However, the suggested criterion is not (provably) suf …
Robert Furber's user avatar
6 votes

About the category of von neumann algebras

I agree with Dmitri Pavlov that separability is not so important in the modern theory of von Neumann algebras, and this answers the second question. However, an example answering the first question ha …
Robert Furber's user avatar
6 votes
Accepted

Examples of non-isomorphic $C^\ast$ algebras with isomorphic quasi-state spaces

For any C$^*$-algebra $A$, we can define its opposite algebra $A^{\mathrm{op}}$, which is the algebra where $ab$ is defined to be $ba$, as calculated in $A$. Let's restrict to unital algebras for simp …
Robert Furber's user avatar
1 vote

Topology of ${\mathcal D}(\Omega)$ (space of test functions)

There's a general principle for proving that a topology on a vector space $E$ is not a weak topology (in the general sense, a topology of the form $\sigma(E,F)$ for some $F \subseteq E^*$). For $\sigm …
Robert Furber's user avatar
5 votes
Accepted

Is the compact-open topology on the dual of a separable Frechet space sequential?

Yes. In the next paragraph I will show that if $X$ is a Fréchet space (without requiring separability) then $X'_c$ with the compact-open topology is a $k$-space. As you note, this implies sequentialit …
Robert Furber's user avatar
10 votes
Accepted

Banach space with uncountable basis

I will pull together the comments into a community wiki answer with some of my own remarks so that the question isn't left on the unanswered questions list. If you're willing to accept that it is cons …

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