Almost conformal transformation in a four dimensional Riemannian   manifold with an additional structure
  We consider a four dimensional Riemannian manifold M with a metric g and affinor structure q. The local coordinates of these tensors are circulant matrices. Their first orders are (A, B, C, B), A, B, C\in FM and (0, 1, 0, 0), respectively.   We construct another metric \tilde{g} on M. We find the conditions for \tilde{g} to be a positively defined metric, and for q to be a parallel structure with respect to the Riemannian connection of g.   Further, let x be an arbitrary vector in T_{p}M, where p is a point on M. Let \phi and \phi be the angles between x and qx, x and q^{2}x with respect to g. We express the angles between x and qx, x and q^{2}x with respect to $\tilde{g}$ with the help of the angles $\phi$ and \phi.   Also,we construct two series {\phi_{n}}and {\phi_{n}}. We prove that every of it is an increasing one and it is converge. 
Iva Dokuzova
math.DG