  Under the influence of Gauss and Grassmann, Riemann’s great  philosophical contribution consisted in the demonstration that,  unlike the case of a discrete manifold, where the determination of a  set necessarily implies the determination of its quantity or cardinal number, in the case of a continuous manifold, the concept of such a  manifold and of its continuity properties, can be separated form its  metrical structure. Using modern terminology, Riemann separated a  manifold’s local differential topological structure from its metrical structure. Thus Riemann’s separation thesis gave rise to the  space problem, or as Weyl called it, das  Raumproblem: how can metric relations be determined on a  continuous manifold \(M\)? 