1 “... results of Krein and H. Langer. Together with our colleagues, we have worked in this area for nearly...”

2 “..., but due to the profusion of results in this area of analysis, the number of topics grew larger than ex...”

3 “... consists oforiginal research papers presenting the stateofthe art in the area ofdifferential operators...”

4 “.... It focusses on the areas of his unusually wide interests and consists of 18 mathematical papers in spectral...”

5 “... and operator theory, especially to the areas in which Peter contributed so richly. At our request, Peter agreed...”

6 “... experts in operator theory. The topics reflect the wide range and the rich variety of areas of interests...”

7 “... and operator functions. Such problems appear in various areas of ma- ematics and its applications...”