The distribution of the eigenvalues of differential operators has long fascinated mathematicians. Advances have shed light upon classical problems in this area, and this book presents a fresh approach, largely based upon the results of the authors. The emphasis here is on a topic of central importance in analysis, namely the relationship between i) function spaces on Euclidean n-space and on domains; ii) entropy numbers in quasi-Banach spaces; and iii) the distribution of the eigenvalues of degenerate elliptic (pseudo) differential operators. The treatment is largely self-contained and accessible to non-specialists. Both experts and newcomers alike will welcome this unique exposition.

Review of the hardback:‘… a fresh approach.’

Source: L'Enseignement Mathématique

Review of the hardback:‘The authors’ mastery of the subject is obvious, and they make every effort to guide the reader through the difficult analysis … The book is recommended to anyone with an interest in function spaces and differential equations.’

W. D. Evans Source: Bulletin of the London Mathematical Society

Review of the hardback:‘… not only an excellent research monograph but also an appropriate introduction to the field.’

H. G. Feichtinger Source: International Mathematical News