Extensions of valuations

نویسنده

  • Jean Goubault-Larrecq
چکیده

Continuous valuations have been proposed by several authors as a way of modeling probabilistic non-determinism in programming language semantics. Let (X;O) be a topological space. A quasi-simple valuation on X is the sup of a directed family of simple valuations. We show that quasisimple valuations are exactly those valuations that extend to continuous valuations to the Alexandroff topology on the specialization preordering of the topology O. A number of applications are presented. In particular, we retrieve Jones’ result that every continuous valuation is quasi-simple if X is a continuous dcpo—in this case, there is a least extension to the Alexandroff topology. We show that this can be refined if X is algebraic, where every continuous valuation is the sup of a directed family of simple valuations based on finite elements. We exhibit another class of spaces where every continuous valuation is quasi-simple, the so-called finitarily coherent spaces—in this case, there is a largest extension to the Alexandroff topology. In general, the extension to the Alexandroff topology is not unique, unless the original valuation is bicontinuous for example. We also show that other natural spaces of valuations, namely those of discrete valuations and point-continuous valuations, can be characterized by similar extension theorems.

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عنوان ژورنال:
  • Mathematical Structures in Computer Science

دوره 15  شماره 

صفحات  -

تاریخ انتشار 2005