Characterizations of complex space forms by means of geodesic spheres and tubes
We prove that a connected complex space form (,g,J) with n ≥ 4 can be characterized by the Ricci-semi-symmetry condition and by the semi-parallel condition , considering special choices of tangent vectors to small geodesic spheres or geodesic tubes (that is, tubes about geodesics), where , and denote the Riemann curvature tensor, the corresponding Ricci tensor of type (0,2) and the second fundamental form of the spheres or tubes and where acts as a derivation.