This issue is the third in a series of direct submissions (Volume 266, issue 3) in the Journal of Mathematical Sciences (Series A). It consists of ten research articles and one review article. Contributing authors are from Portugal, Israel, Russia, Kazakhstan, Argentina, China, Turkey, Uzbekistan, Algeria. Guest editors: A. Almeida (Portugal), Z. Kusraeva (Russia) and H. Rafeiro (UAE).

The issue is a thematic one dedicated to Professor Stefan Samko on the occasion of his 80th anniversary. This issue appeared within the activities of the OTHA-2021 conference, dedicated to the 80th anniversary of Professor Samko.

Professor Stefan Samko, born on March 28, 1941, is a Russian and Portuguese mathematician. He is a world-leading specialist in various areas of analysis and applications, including fractional integrodifferentiation, theory of functions and function spaces, operator theory, analysis of variable order, and many other areas of mathematics. He supervised numerous PhD students who now work in various countries of the world. Most recent achievements of professor Samko can be found in the review article written by the guest editors, A. Almeida, Z. Kusraeva and H. Rafeiro. It is available for open access, see PROFESSOR STEFAN G. SAMKO RESEARCH: A DECADE RETROSPECTIVE | SpringerLink

This is not the only collection that has been prepared as a thematic issue related to research interests and achievements of S.Samko. An analogous topical collection appeared recently under the editorship of A. Karapetyants, V. Kravchenko and E. Liflyand in the Journal of Fourier Analysis and Applications (JFAA), see https://link.springer.com/journal/41/topicalCollection/AC_818336f0e80a0906b1769983284fa4f6/page/1