Foreword

This essay is dedicated in admiration to the memory of Gilles Kahn, a friend and guide for 35 years. I have been struck by the confidence and warmth expressed towards him by the many French colleagues whom he guided. As a non-Frenchman I can also testify that colleagues in other countries have felt the same.

I begin by recalling two events separated by 30 years; one private to him and me, one public in the UK. I met Gilles in Stanford University in 1972, when he was studying for the PhD degree – which, I came to believe, he found unnecessary to acquire. His study was, I think, thwarted by the misunderstanding of others. I was working on two different things: on computer-assisted reasoning in a logic of Dana Scott based upon domain theory, which inspired me, and on models of interaction – which I believed would grow steadily in importance (as indeed they have). There was hope to unite the two. Yet it was hard to relate domain theory to the non-determinism inherent in interactive processes. I remember, but not in detail, a discussion of this connection with Gilles. The main thing I remember is that he ignited. He had got the idea of the domain of streams which, developed jointly with David MacQueen, became one of the most famous papers in informatics; a model of deterministic processes linked by streams of data.