Valentin A. Zagrebnov  is an Emeritus Professor of Aix-Marseilles University. He is a member of the Institut de Mathématiques de Marseille - UMR 7373 and its research group on Analysis, Geometry and Topology. His research interests include Functional Analysis and Semigroup Theory. In particular they are concentrated around Gibbs semigroups, Trotter-Kato product formulæ and semigroup approximations developing the Chernoff method; non-autonomous Cauchy problem and the product formula construction of solution operators. Hagen Neidhardt  worked from 1975 to 1991 as a research assistant at the Karl-Weierstraß-Institut für Mathematik of the Academy of Sciences of the GDR in Berlin, in the group "Operator Theory and Mathematical Physics" led by Professor Hellmut Baumgärtel. In 1992-1993 Neidhardt worked as a research assistant in the Mathematics Department at the Technical University of Berlin and then in the Mathematics Department at the University of Potsdam (1994-1999). From 2000 and until his professional retirement in 2016, he returned as scientific staff member to the Weierstraß-Institut für Angewandte Analysis und Stochastik (WIAS) in Berlin. Neidhardt was a world-renowned expert in the areas of functional analysis, operator theory and mathematical physics, where he made a number of highly original contributions. Several mathematical concepts were named after Hagen Neidhardt. They are the Koplienko-Neidhardt trace formula and also the Howland-Evans-Neidhardt formula and approach to evolutionary equations in Hilbert space. Takashi Ichinose  is an Emeritus Professor of Kanazawa Universoty, Kanazawa, Japan. His research interests include all sorts of problems in functional analysis, operator theory, partial differential equations and functional integration appearing in mathematical physics.