Ein einfacher Beweis des Satzes von Alexandroff-Lester. (A simple proof of the theorem of Alexandroff-Lester)
Assume V is an at least 3-dimensional vector space, Q is a quadratic form on V, there are nontrivial singular vectors in V but not in the radical of V. Then every 0-isomorphism is a metric automorphism with respect to Q. The author gives a new, short, and transparent proof for this theorem. Examples show the necessity of the assumptions.
scientific article; zbMATH DE number 4155322