Special issue dedicated to the 60 th birthday of Etienne E .

The year 2005 is marked by the 40th anniversary of fuzzy set theory, as it was in 1965 that Lotfi Zadeh published his famous seminal paper that fostered the rise of a whole new community, researching theory and applications of fuzzy sets and systems. Throughout the years, fuzzy logic was frequently met with skepticism, not in the least because of its often misunderstood name. Nevertheless, our research community survived and grew to its full potential thanks to a few brave researchers who did ground breaking work in those early years – the pioneers of fuzzy logic. One of those pioneers is Etienne E. Kerre. Etienne was born on May 8, 1945 in Zele, Belgium, studied mathematics at Ghent University and obtained his PhD degree there in 1970 for research on “Low Energy Electron Diffraction”. Soon after, he started research in fuzzy set theory, founding the Fuzziness and Uncertainty Modelling Research Unit in 1976, while in 1978 he organized and taught the first “free course” on the theory of fuzzy sets. Etienne soon gained a reputation as a passionate and gifted lecturer, and currently teaches mathematical analysis to the undergraduates in computer science as well as fuzzy set theory at the graduate and postgraduate level in mathematics and computer science. Celebrating his 60th birthday on May 8, 2005, Etienne has a very rich research career to look back on. His extensive list of over 350 publications shows an evolving interest in a wide variety of topics, including fuzzy topology, fuzzy databases, fuzzy logical operators, fuzzy rough sets, and many, many more. Indeed, the overview of Etienne’s research output is a good reflection of many important topics and problems that puzzled our community the past decades; realizing this inspired us to compose this special issue. Etienne is known to be very concerned with the young people carrying out research under his supervision. Their worries deprive him of sleep, their successes make him immensely proud, helping them in their research and their careers is his highest priority. We therefore decided to present a compilation of Etienne’s work in terms of the twenty researchers who so far have completed their PhD under Etienne’s guidance. In particular, a call for papers was targeted at those past PhD students, inviting them to submit research papers describing recent results they and their collaborators obtained within the wide domain of fuzziness and uncertainty modelling. Many enthusiastic reactions ensued, and, after a thorough and rigourous reviewing process, made possible by the efforts of fifteen anonymous referees, seven original contributions were accepted for publication. They cover several of the theoretical and applied domains Etienne has helped shape – including fuzzy database and ER models, intervalvalued fuzzy set theory, fuzzy techniques for image processing, and fuzzy relational calculus – and most of all, they are written according to the rigorous and elegant mathematical tradition so characteristic of Etienne’s style. Finally, we tracked down each of those twenty people to see how they have fared in life after their PhD. Some