The C* -algebra extensions of a topological space can be made into an abelian group which is naturally equivalent to the Khomology group of odd dimension [1] which has a close relation with index theory and is one of the starting points of KK theory [8]. The Cp -smoothness of an extension of a manifold was introduced in [3, 4], where Cp denotes the Schatten-von Neumann p-class [5]. We generaliz...