e-= 1}. In this paper, a geometry characteristic for E is presented by using a geometrical construct of S(E). That is, the following theorem holds: the norm of E is of c 1 in E\{0} if and only if S(E) is a c 1 submanifold of E, with codimS(E) = 1. The theorem is very clear, however, its proof is non-trivial, which shows an intrinsic connection between the continuous differentiability of the norm ‖·-in E\{0} and differential structure of S(E)." />