Wilker property, function spaces and hyperspaces

Abstract

The Wilker property requires that a compact set covered by two open sets admit compact covering pieces inside those open sets. We study this property through products, compact-open function spaces and hyperspaces. We construct countable compact Fréchet--Urysohn $T_1$ hereditarily Wilker spaces with non-Wilker products and squares. For spaces whose compact subsets are closed, Wilker-ness is equivalent to every compact subspace being Hausdorff; this yields a positive product theorem when one Wilker factor has closed compact subsets. For an irreducible subset system $H$, we characterize preservation of $H$-sobriety by compact-open function spaces in terms of $H$-supercompactness of compact subsets of the domain, and show that Wilker spaces satisfy this criterion. The Hoare hyperspace of a space is Wilker exactly when binary union on the Scott space of its open-set lattice is jointly continuous for the ordinary product topology. Consequently, the Hoare construction preserves and reflects Wilker-ness on consonant bases, although preservation fails in general. We also identify core-compactness of the base with local compactness of its Hoare hyperspace and prove that the Smyth construction reflects Wilker-ness.