The relations between ultracompactness of topological spaces and ultraClosedness of mappings, are further studied in this paper. The properties of ultraclosed mappings are displayed. An expression of D-limits of nets ...
In this paper,we study mainly properties of a class approx mate ope rator in Hilbert space, form as S=T+Q where T is a power class (N) operator and Q is a quasinilpotent opera tot with TQ=QT. We discuss relation of ke...