title: Two theorems in catoptrics.
abstract: Two general theorems in the theory of mirrors are presented. The first one asserts that a mirror that reflects a parallel beam into a beam with zero mean curvature must be harmonic. The second one provides a universal characterization of the spot diagram of rays from a reflected parallel beam as they intersect a plane orthogonal to their direction of propagation.
authors.affiliation: Department of Mathematics, Technion-Israel Institute of Technology, Haifa. koby@math.technion.ac.il
authors.forename: J
authors.initials: J
authors.lastname: Rubinstein
authors.forename: G
authors.initials: G
authors.lastname: Wolansky