In this paper, we deal with the problem of uniqueness of meromorphic functions that share three sets and obtain some unicity theorems which improve some theorems given by F. Gross and C. F. Osgood, K. Tohge, G. Brosch, G. Jank and N. Terglane, H. X. Yi and other authors.
O'Neill introduced a notion of Riemannian submersion [7]. In this paper we give a new notion of semi-Riemannian submersion and want to investigate some geometric properties concerned with sectional and Ricci curvatures of this submersion.