Examples of semi-ovoids are the sets of isotropic points of an hermitian form. They are called hermitian quadrics. As for ovoids in literature there are criteria, which make a semi-ovoid to a hermitian quadric. See, for example. Semi-ovoids are used in the construction of examples of Möbius geometries. See also Ovoid (polar space) Möbius plane Notes References Further reading External links E. Hartmann: Planar Circle Geometries, an Introduction to Moebius-, Laguerre- and Minkowski Planes. Skript, TH Darmstadt (PDF; 891 kB), S. 121-123. Projective geometry Incidence geometry