a closed hyperbolicmanifold http://arxiv.org/abs/0910.5501 (页面存档备份,存于互联网档案馆), Counting essential surfaces in a closed hyperbolic3-manifold, http://arxiv
(often abbreviated to dSn) is a maximally symmetric Lorentzian manifold(英语:Lorentzian manifold) with constant positive scalar curvature(英语:scalar curvature)