On Wigner's theorem: Remarks, complements, comments, and corollaries
The author uses functional equations to present a very simple proof of Wigner's unitarity-antiunitarity theorem (simultaneously in the real and the complex case) and it is shown how some hypotheses (like the completeness of the inner product spaces) can be eliminated. Some connections with special classes of geometrical transformations are given.
Wigner's unitarity-antiunitarity theorem
scientific article; zbMATH DE number 935124