A Monotone Selection Principle in C*-algebras

Abstract

We apply to operator algebra theory a monotone selection principle which apparently escaped attention (of operator algebra theorists) so far. This principle relates to the basic order theoretic characterisation of von Neumann algebras given by Kadison, and the simplified form this result takes in separable Hilbert spaces. In the separable case we need only consider increasing sequences rather than increasing nets. We apply an argument of Klaus Floret to show that, within the realm of commutativity, there exists a general monotone selection principle providing for this simplification. Thereby we obtain a valuable shortcut and a handy tool for related purposes. Actually, a more general selection principle is proved within the framework of vector lattices.