  Gaussian curvature of the two-surface r=0, t=const is calculated for the
Kerr-de Sitter and Kerr-Newman-de Sitter solutions, yielding non-zero
analytical expressions for both the cases. The results obtained, on the one
hand, exclude the possibility for that surface to be a disk and, on the other
hand, permit one to establish a correct geometrical interpretation of that
surface for each of the two solutions.
