EPIREFLECTIVE HULLS OF SPACES OF ORDINALS IN T_o

Abstract

A particular class of epireflective subcategories of To is investigated, exactly the epireflective hulls g(S(a) of the spaces S(a) of the ordinals with the “open half lines” topology. The topological structure of the objects of these hulls is studied, also in relation with their sobrification. Furthermore, a bijective correspondence between hulls and classes of cofinality of ordinals is found.