We prove that if X is a Banach space, R, S ∈ B(X), then RS is subscalar (subdecomposable) if and only if SR is. As corollaries, it is shown that w-hyponormal operators (including p-hyponormal (p > 0) and log-hyponormal operators) and their Aluthge transformations and inverse Aluthge transformations are subscalar. (2000). Primary 47B99; Secondary 47A10.
Mathematics Subject Classification
A Banach space X has property (K), whenever every weak* null sequence in the dual space admits a convex block subsequence (f n ) ∞ n=1 so that f n , x n → 0 as n → ∞ for every weakly null sequence (x n ) ∞ n=1 in X; X has property (µ s ) if every weak * null sequence in X * admits a subsequence so that all of its subsequences are Cesàro convergent to 0 with respect to the Mackey topology. Both property (µ s ) and reflexivity (or even the Grothendieck property) imply property (K). In the present paper we propose natural ways for quantifying the aforementioned properties in the spirit of recent results concerning other familiar properties of Banach spaces.
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