The converse Ostrowski theorem

Abstract

The Ostrowski theorem in question is that an additive function bounded (above, say) on a set T of positive measure is continuous. In the converse direction, recall that a topological space T is pseudocompact if every function continuous on T is bounded. Thus theorems of `converse Ostrowski' type relate to `additive (pseudo)compactness'. We give a different characterization of such sets, in terms of the property of `generic subuniversality', arising from the Kestelman-Borwein-Ditor theorem