On summability domains

Abstract

We denote by ω the space of all complex sequences with the topology given by the semi-normswhere δn(x) = xn. An FK-space, E, is a subspace of ω on which there exists a complete metrizable locally convex topology τ, such that the inclusion (E, τ) ⊂ ω is continuous; if τ is given by a single norm then E is a BK-space.