On February 7, 2023, an editorial letter was issued in memory of Clemens Heine, Managing Editor of Applied Mathematics / Computer Sciences, Birkhäuser.

This issue is the first in a series of direct submissions making the Journal of Mathematical Sciences an excellent new platform for the publication of high-quality papers submitted by scientists from all over the world. The present issue, the first in this series, is dedicated to the memory of the Doctor of Sciences, Professor N.K. Karapetyants (1942-2005).

This issue is the third in a series A of direct submissions. The issue is a thematic one dedicated to the Doctor of Sciences, Professor Stefan Samko. We are happy to express appreciation to the excellent team of guest editors, A. Almeida (Portugal), Z. Kusraeva (Russia), and H. Rafeiro (UAE), who collected the articles and organized a peer-review process for the issue.