Yesterday, 21 October 2017, our dear friend and colleague Kosta Dosen passed away; losing his long struggle with cancer. He is survived by his daughter Ana. The service and funeral will take place at the New Cemetery in Belgrade on 24 October 2017, 12:00 (noon). Born 1954 in Belgrade (Serbia), Kosta Dosen graduated from the University of Belgrade in 1977 and received a doctorate from the University of Oxford in 1981. He became a professor at the Mathematical Institute Belgrade in 1982, was professor at the Department of Computer Science of the University of Toulouse (France) from 1994 to 1998, and held the Chair of Logic in the Philosophical Faculty of the University of Belgrade since 2003. He had visiting posts at universities including Notre Dame (USA), Montpellier (France) and Tuebingen (Germany). Kosta Dosen's D.Phil. on "Logical Constants" was supervised by Michael Dummett and Dana Scott. As part of this, and in subsequent publications, he developed a proof-theoretic characterization of logical constants by means of so-called "double-line rules", which has become widely discussed since and is one of the major approaches in the debate on what logicality should mean. Working on the proof theory (and partly also model theory) of logics with restricted structural rules, he coined the term "substructural logic" at a conference in Tuebingen in 1990. However, the main topic of his intellectual life was the field of categorial proof theory that was opened up by Lambek, Lawvere and others. Kosta Dosen shaped the development of this field in many respects, in particular by his books on "Cut Elimination in Categories" and "Proof-Theoretical Coherence" (the latter together with Zoran Petric). He was a strong adherent and promotor of what Prawitz called "general proof theory", which is the study of proofs as objects in their own right rather than under the aspect of provability. This implied for him that the question of the identity of proofs was the central topic of general proof theory, where he was particularly interested in the relationship between normalization-based and generality-based approaches. In recent years he worked with great passion on Goedel's work including unpublished manuscripts in his Nachlass. A critical edition (together with Milos Adzic) of Goedel's Notre Dame course in logic has just appeared. Kosta Dosen was a gifted and dedicated teacher, who was an inspiration to students and colleagues alike. His explanations will live on in the pages of his textbook on elementary logic (in Serbian). A further, and more thorough discussion of Kosta Dosen's achievements will be published at a later stage. Kosta will be greatly missed by relatives, friends and colleagues, and all who had the good fortune to know him. -- Prof. Peter Schroeder-Heister Department of Computer Science University of Tuebingen Sand 13 72076 Tuebingen Germany e-mail: psh@uni-tuebingen.de http://ls.inf.uni-tuebingen.de [For admin and other information see: http://www.mta.ca/~cat-dist/ ]