A classsical theorem of A. D. Alexandrov characterizing round spheres is extended to the complex hyperbolic space CH2 of constant holomorphic sectional curvature. A detailed description of the horospheres and equidistant hypersurfaces in CH2 determining in particular their stability, is also given.
Cadernos de matemática e estatística. Série A, Trabalho de pesquisa. Porto Alegre. N. 20 (ago. 1991), p. 1-28.