Algebraisch spezielle Einstein-Räume mit einer Bewegungsgruppe

In algebraically special Einstein spaces (R_v=0) with a hypersurfaceorthogonal spacelike Killing vector field _v, the trajectories of the multiple eigen null directions k lie — except one case — in the subspacesV ₃ orthogonal to _v (k=0) and are hypersurface-orthogonal. The solutions with vanishing expansion (k_,;=0, Kundt's class) can be determined explicitly.