Our collaboration with Arren had a somewhat turbulent start, when he as a young group leader was afraid we could « beat » him on one of his key research topics. Not only that beating Arren on his scientific playground was simply impossible, we were able to calm down the storm quickly and entered into an extremely fruitful and pleasant partnership, where we plainly benefitted from his ideas, his generosity and his attaching character. Needless to say how much we already miss him. He is gone far too early, but his spirit remains. Volker and Madeleine