Some comments on regular and normal bitopological spaces

Some properties of regular and normal bitopological spaces are established. The classes of sets inheriting the bitopological properties of regularity and normality are found. A theorem on a finite covering of pairwise normal spaces is proved. We also study the behavior of individual multivalued mappings, taking the axioms of bitopological regularity and normality into account. Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, No. 12, pp. 1720–1724, December, 2006.     

Some results on the convexity of the closure of the domain of a maximally monotone operator

We provide a concise analysis about what is known regarding when the closure of the domain of a maximally monotone operator on an arbitrary real Banach space is convex. In doing so, we also provide an affirmative answer to a problem posed by Simons.     

The closure operator in a multivalued logic based on functional equations

An operator of FE-closure is introduced on the set of functions of a multivalued logic based on the systems of functional equations. It is proved that, for every k ≥ 2, the FE-closure operator generates a finite classification on the set P _k of functions of k-valued logic. The least class in this classification is shown to be the class H _k of all homogeneous functions. Also a series of corollaries are obtained concerning the finite FE-generating sets in the FE-closed classes.     

Some remarks on interior operators and the functional property

In this paper functoriality of the notion of categorical interior operator is discussed and as a related topic, the property of ?-modal interior operator is introduced.     

Equational closure operator and forbidden semidistributive lattices

Dedicated to the memory of A. I. Mal'tsev.     

Some remarks on the operator of Foias and Williams

In this paper we study the Foias-Williams operator

where , and is a Hankel operator with symbol . We exhibit a relationship between the similarity of to a contraction and the rate of decay of , the absolute values of the Fourier coefficients of the symbol .

     

On the concepts of intertwining operator and tensor product module in vertex operator algebra theory

We produce counterexamples to show that in the definition of the notion of intertwining operator for modules for a vertex operator algebra, the commutator formula cannot in general be used as a replacement axiom for the Jacobi identity. We further give a sufficient condition for the commutator formula to imply the Jacobi identity in this definition. Using these results we illuminate the crucial role of the condition called the “compatibility condition” in the construction of the tensor product module in vertex operator algebra theory, as carried out in work of Huang and Lepowsky. In particular, we prove by means of suitable counterexamples that the compatibility condition was indeed needed in this theory.     

The pullback closure operator and generalisations of perfectness

A categorical closure operator induced via pullback by a pointed endofunctor is introduced. Various notions of a perfect morphism relative to a pointed endofunctor and the induced closure are then considered. The main result explores how these notions are interrelated, linking also with earlier notions of perfectness.The author acknowledges financial support from the University of Cape Town, from the Foundation for Research Development through the Categorical Topology Research Group at the University of Cape Town, and from the University of L'Aquila.     

Some remarks on operator ranges

Translated from Teoriya Funktsii, Funktsional'nyi Analiz i Ikh Prilozheniya, No. 53, pp. 69–70, 1990.     

SOME RESULTS ON THE REFLEXIVITY OF OPERATOR SUBSPACES

In this paper, the properties B^n p,q, and B^n 1,q are introduced.A lot of results on the reflexivity of operator operator subspaces which generalize the results in [1] are obtained.     

On the bounded closure of the range of an operator

The ``bounded closure of the range" of an operator between two normed spaces is a linear subspace lying between the range and its closure. The induced concept of ``almost onto" is a sort of first draft of the concept of ``almost open".

     

Neighborhoods and convergence with respect to a closure operator

We study neighborhoods with respect to a categorical closure operator. In particular, we discuss separation and compactness obtained from neighborhoods in a natural way and compare them with the usual closure separation and closure compactness. We also introduce a concept of convergence based on using centered systems of subobjects, which naturally generalizes the classical filter convergence in topological spaces. We investigate behavior of the convergence introduced and show, among others, that it relates to the separation and compactness in natural ways.     

Problems of the theory of bitopological spaces

This paper gives a survey of and problems in the study of bitopological spaces.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 167, pp. 5–62, 1988.     

Some functional equations on standard operator algebras

The main purpose of this paper is to prove the following result. Let H be a complex Hilbert space, let (H) be the algebra of all bounded linear operators on H, and let (H) ⊂ (H) be a standard operator algebra which is closed under the adjoint operation. Suppose that T: (H) → (H) is a linear mapping satisfying T(AA* A) = T(A)A* A − AT(A*)A + AA*T(A) for all A ∈ (H). Then T is of the form T(A) = AB + BA for all A ∈ (H), where B is a fixed operator from (H). A result concerning functional equations related to bicircular projections is proved