General methods of investigating effectivity on regular Haus-dorff (T 3 ) spaces is considered. It is shown that there exists a functor from a category of T 3  spaces into a category of domain representations. Using this functor one may look at the subcategory of effective domain representations to get an effectivity theory for T 3  spaces. However, this approach seems to be beset by some problems. Instead, a new approach to introducing effectivity to T 3  spaces is given. The construction uses effective retractions on effective Scott-Ershov domains. The benefit of the approach is that the numbering of the basis and the numbering of the elements are derived at once.
['Jens Blanck']
Effectivity of regular spaces