Equivalence of topologies and Borel fields for countably-Hilbert spaces. (English) Zbl 1081.57019

The author examines the main topologies – weak, strong, and inductive – placed on the dual of a countably-normed space and the \(\sigma\)-fields generated by these topologies. In particular, he proves that for certain countably-Hilbert spaces the strong and inductive topologies coincide and the \(\sigma\)-fields generated by the weak, strong, and inductive topologies are equivalent.
The author motivates his study as follows: “Although these results have been used implicitely or explicitely in the literature, there appears to be no efficient or complete proof published or readily accessible without having to work through a vast literature. It is the purpose of this paper to present proofs of these results in a largely self-contained manner. For this reason we have included here proofs of various well-known results; these proofs serve the function of setting up arguments and notation for our principal objectives.”
The main results consist in the statement and the proof of the following theorems.
Theorem 4.16. Let \(V\) be a countably-Hilbert space with dual \(V'\). Then the inductive, strong, and Mackey topologies on \(V'\) are equivalent (i.e. \(\tau_s= \tau_i= \tau_m\)).
(The Mackey topology on a topological vector space \(E\) with dual \(E'\) is the topology of uniform convergence on all balanced convex weakly-compact subsets of \(E'\) [cf. Section 21.4 in G. Köthe, Topological vector spaces. I (Springer-Verlag, Berlin) (1969; Zbl 0179.17001)].)
Theorem 5.3. Let \(V'\) be the dual of a countably-Hilbert space \(V\) which has a countable dense subset. Suppose V’ to be endowed with a topology \(\tau\). If \(\tau\) is finer that \(\tau_w\) and the inclusion map \(i_n': V_n'\to V'\) is continuous for all \(n\), then the \(\sigma\)-fields generated by \(\tau\) and \(\tau_w\) are equal (i.e. \(\sigma(\tau_w)= \sigma(\tau)\)). In particular, the \(\sigma\)-fields generated by the inductive, strong, and weak topologies on \(V'\) are equivalent (i.e. \(\sigma(\tau_w)= \sigma(\tau_s)= \sigma(\tau_i)\)).
(The dual countably-normed space \(V\) is given by \(V'=\bigcup^\infty_{n= 1} V_n'\) with the inclusions \(V_1'\subset\cdots \subset V_n'\subset V_{n+1}'\subset\cdots\subset V'\), cf. Prop. 3.6 in the paper.)
Reviewer: Ioan Pop (Iaşi)


57N17 Topology of topological vector spaces
60H40 White noise theory
54A10 Several topologies on one set (change of topology, comparison of topologies, lattices of topologies)
46A99 Topological linear spaces and related structures


Zbl 0179.17001
Full Text: DOI


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