I first met Chris at a Conference organized by Rudy Kalman in 1977. At that time, our research interests were quite apart. I met him again in 1979, at a Conference he had co-organized at Harvard University, and then subsequently at a Conference that I had co-organized in Rome in 1981. At that time our research interests begun to converge and eventually I invited him for a sabbatical at the University of Rome, in spring 1983. This visit marked the beginning of a mutually rewarding and long-lasting scientific collaboration. One day in 1988, walking on the shores of a beach in southern France, when we both were attending the bi-annual Control Conference organized by INRIA, Chris explained to me that the most appropriate mathematical tool for the solution of the problem of shaping the steady state response of nonlinear systems was the so-called Center Manifold Theorem. This was an intuition full of consequences.  In fact, center manifold theory proved instrumental in deriving necessary conditions for the existence of a “local” regulator. These eventually became known as the “nonlinear regulator equations” and nicknamed as FBI equations, after Francis, Byrnes and Isidori.

When he become Dean of Engineering at Washington University, our scientific collaboration continued, but at an obviously lesser level. However, he was always a source of ideas and intuitions. For instance, in the early 2000’s, it was again Chris’ intuition the prime mover behind a series of papers which use some advanced concepts from the theory of dynamical system, such as the concept of limit set of a set, to the purpose of proving a general, non local, non-equilibrium based, approach to the design of regulators.

His enthusiasm, passion and sense of humor were constantly the right catalyst in a series of unforgettable scientific adventures. In the words of his last student, he was “a great scholar, a gracious host, and a fine man”. He has been part of my personal life for many years, scientifically and socially. Last December, when I saw him last time in Shanghai at our annual IEEE Control Conference, we planned a number of joint activities for this coming spring, which included the preparation of new joint paper. I miss him enormously.