1 Professor Da Ruan, Distinguished Visitor at Complutense University, Madrid Javier Montero 1 Begoña Vitoriano 2 Daniel Gómez Facultad de Matemáticas Facultad de Matemáticas Escuela de Estadística Universidad Complutense Universidad Complutense Universidad Complutense Madrid 28040, Spain Madrid 28040, Spain Madrid 28040, Spain javier_montero@mat.ucm.es bvitoriano@mat.ucm.es dagomez@estad.ucm.es It is extremely difficult to maintain a strictly academic discourse about a colleague that unexpectedly passed away when he was a friend and when he has been playing a key role in your recent research activities. He will be deeply missed. In this short note we shall bring here some highlights of the relationship between our research team and Da Ruan, starting with our relationship with the International FLINS Conferences (see details of all the FLINS conference since 1994 at http://flins2012.itu.edu.tr/history_of_flins.html ). Since the beginning of the contacts of members of this Complutense University team on Decision Aid Systems with Da Ruan and his collaborators at SCK-CEN and the University of Ghent, the FLINS conference appeared for us as a singular conference, where practitioners and theoretical researchers could find an easy environment for interchanging knowledge and develop joint projects. FLINS initiative (acronym standing for Fuzzy Logic and Intelligent Technologies in Nuclear Science) was launched by 1994 in line with the Belgian Nuclear Research Centre (SCK•CEN) and the initial objective of giving PhD and Postdoc researchers the opportunity to carry out future- orientated research. Since then, objectives have evolved into much wider interests, covering now any research within computational intelligence and knowledge engineering in decision and control, still keeping the foundational declared objective of producing a real advance in the theory and applications of decision making and control for complex systems. Since its conception, Professor Da Ruan put into the organization of each FLINS conference an extremely careful effort to facilitate such a scientific interchange, indeed keeping a kind attention for the needs of all conference attendants to create a good climate for communication. Coming to FLINS conference has been always a wonderful experience, both scientific and personal. Beside such a unique approach for a rather small but still somehow heterogeneous community open to any issue related to complex systems, a number of illuminating talks by colleagues come to our mind. But we have also to remind with pleasure all those scientific discussions we could have with colleagues during FLINS conferences, sometimes around a pot of Belgian mussels, or simple around a beer after the conference, or even walking along a beach or some historical site (needless to say, not taking care too much about the surrounding beauty because of the intense scientific conversation we were having). Such a kind of human relationship between the conference attendants created a quite familiar ambience, which can not be understood without Da’s personality, his continuous smile and the devoted dedication of all his FLINS organization. Particularly, one of the authors of this short note will be always grateful to Da and the FLINS community for the kindness, support and friendship he found in some difficult personal times. We are proud of being part of his FLINS project. 1 Javier Montero has been proudly acknowledged as FLINS Golden Pin (2004) and FLINS Silver Chair (2010), and has been honoured as Local Chair of the 8th FLINS conference held in Madrid (2008). Javier Montero would like to express his personal gratitude and admiration to Da’s wife, Greet, who from her terrible moments helped him so much when he travelled from Spain to Mol, just to say goodbye to Da at the funerarium, a very sad trip. 2 Begoña Vitoriano has been proudly acknowledged as FLINS Silver Pin (2008).