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The theme of this paper is the interaction between analytic properties of (Fréchet) Köthe function spaces X and measure/operator theoretic properties of thecanonical spectral measure Q acting in X. For instance, Q is boundedly σ-additive iff X is Montel. Or, Q has finite variation (for the strong operator topology) iff X is an AL-space. Or, there exist unbounded Q-integrable functions whenever X is nonnormable and has the density condition; this is based on characterizing Q-integrable functions as measurable multipliers.

Keywords: Köthe function space, spectral measure, Q-integrability, density condition

Quaestiones Mathematicae 29(2006), 91–116