über die Reflexion von Geradenbündeln an Flächen

A surface F is reflecting the bundle of straight lines through a fixed point A. The congruence of reflected straight lines is called reflection-congruence. We study its focal points. If each point of F lies in the middle of the two focal points, F is called a reflection-minimal-surface. We determine special reflection-minimal-surfaces among the minimal-surfaces, the ruled surfaces and the rotation surfaces and give a relation between reflection-minimal-surfaces and isotropic minimal-surfaces.