Article
UNITARY EXTENSIONS OF TWO-PARAMETER LOCAL SEMIGROUPS OF ISOMETRIC OPERATORS AND THE KREIN EXTENSION THEOREM
Autor
Bruzual, Ramón
Institución
Resumen
A notion of two-parameter local semigroups of isometric operators in Hilbert space is discussed. It is shown that under certain conditions such a semigroup can be extended to a strongly continuous two-parameter group of unitary operators in a larger Hilbert space. As an application a simple proof of the Eskin bidimensional version of the Krein extension theorem is given.