I was very sad to learn that David had died.  He was Head of Department when I was appointed as a lecturer in 1993 and was somebody I looked up to and admired.  He was a kind and thoughtful man, who took his responsibilities to his staff and his students very seriously and who went out of his way to help people.  Others have spoken of his seminal work in structures and in systems thinking, and like many others I was inspired by him to read widely about systems and to integrate sytems thinking into my work.  His ideas and work live on in the many papers and books that he published so that future generations will also learn from him.  The memorial service held today was a fitting tribute to a man who thought deeply and widely and who will be much missed.  My deepest condolences to Karen and the family.