Published in honour of the 70th birthday of Yoh-Han Pao, George S. Dively Dis­ tinguished Professor of Engineering at Case Western Reserve University, Cleveland, Ohio, this festschrift embraces a remarkably diverse set of topics. Drawing from the fields of pattern recognition, engineering, artificial intelligence and artificial neural systems, it is a fitting testament to the extraordinary breadth of his professional in­ terests both in foundational research into the new technology of Intelligent Systems and ill the application of that evolving technology to the solution of hard engineering problems. In common with many scientists who build their reputations in one field before devoting their considerable energies and talents to another one, by 1972, the year in which I met him for the first time, Yoh-Han had made significant contributions to laser technology, in particular to the development of the highly accurate and stable lasers required for holographic recording purposes. In conventional holography, the information stored in a hologram produces a virtual image of the object charac­ terised by it. However, Yoh-Han became fascinated by the possiblity of driving the process hackwards, of using the hologram as an associative memory device enabling previously stored information to be retrieved on the basis of partial cues. It was this burgeoning interest which shaped his career for more than twenty years. Just prior to 1972, my colleagues Professor Christopher Longuet-Higgins and Dr.