We show that the unit ball of a full Hilbert C∗-module is sequentially compact in a certain weak topology if and only if the underlying C∗-algebra is finite dimensional. This provides an answer to the question posed in J. Chmieliński et al [Perturbation of the Wigner equation in inner product C∗-modules, J. Math. Phys. 49 (2008), no. 3, 033519].

We prove a related fixed point Theorem for four mappings which are not continuous in four fuzzy metric spaces, one of them is a sequentially compact fuzzy metric space. Our Theorem in the metric version generalizes Theorem 4 of [1]. Finally, We give a fuzzy version of Theorem 3 of [1].

We study the farthest point mapping in a p-normed space X in virtue of subdifferential of rx sup{{x − z p : z ∈ M}, where M is a weakly sequentially compact subset of X. We show that the set of all points in X which have farthest point in M contains a dense G δ subset of X.

Motivated by questions in stability theory for hybrid dynamical systems, we establish some fundamental properties of the set of solutions to such systems. Using the notion of a hybrid time domain and general results on set and graphical convergence, we establish under weak regularity and local boundedness assumptions that the set of solutions is sequentially compact and “upper semicontinuous” w...

Definition 1.1 (Compact and Totally Bounded Sets). Let X be a metric space, and let E ⊆ X be given. (a) We say that E is compact if every open cover of E contains a finite subcover. That is, E is compact if whenever {Uα}α∈I is a collection of open sets whose union contains E, then there exist finitely many α1, . . . , αN such that E ⊆ Uα1 ∪ · · · ∪ UαN . (b) We say that E is sequentially compac...

Let C be a compact convex subset of a Hausdorff topological vector space (E , τ) and σ another Hausdorff vector topology in E . We establish an approximate fixed point result for sequentially continuous maps f : (C , σ) → (C , τ). As application, we obtain the weakapproximate fixed point property for demicontinuous self-mapping weakly compact convex sets in general Banach spaces and use this to...

This paper considers some typical optimal control problems for a class of strongly nonlinear parabolic systems. After some necessary preparation, it is shown that the family of admissible trajectories is a weakly closed and weakly sequentially compact subset of a reflexive Banach space and that the set of attainable states at any given time is a weakly compact subset of a Hilbert space. Using t...

Cardinal invariants related to sequential separability of generalized Cantor cubes 2κ, introduced by M. Matveev, are studied here. In particular, it is shown that the following assertions are relatively consistent with ZFC: (1) 2ω1 is sequentially separable, yet there is a countable dense subset of 2ω1 containing no non-trivial convergent subsequence, (2) 2ω1 is not sequentially separable, yet ...