The material of the book is very carefully developed and even includes an introduction into the basics of topological and metric spaces. At the beginning of each chapter, a brief outline of the subjects treated therein is given, while at the end, notes, comments and suggestions for further reading are included. The book ends with an extensive reference list, an index and a very helpful index of notations. (Wolfgang Lusky, Mathematical Reviews, December, 2021)
The book may be highly recommended to all students and researchers with some knowledge of Banach or Hilbert space oriented functional analysis who want to learn its general abstract foundations. (Jochen Wengenroth, zbMATH 1453.46001, 2021)