"The study of relative topological properties was initiated by Arhangel’skii and H.M.M. Genedi in their seminal paper . They studied the following general problem: Given a topological property P and a subspace Y of a topological space X, how can we define a property P0, in terms of location of Y, in a natural way so that P0 coincides with P if Y Æ X? In this way, they considered different properties, which include separation axioms and compactness type properties. Of course, relative topological properties often generalize a global property in the sense that if the smaller space Y coincides with the larger space X, then the relative topological property should be the same as the global one."