Leo died more than 35 years ago, before his 49th birthday, and he has been in my thoughts and memory all these years. Leo was my first mathematical mentor. When I was a teenager he was already showing me the pleasures of mathematics. Leo's enthusiasm for mathematics was boundless, his creativity was ingenious, and creating problems was his specialty. In this respect he was like Paul Erdős, whom Leo greatly admired (as did I); and like Erdős he was completely open and generous with his knowledge.

In August 1949 I participated in a meeting of the Canadian Mathematical Congress in Vancouver. This organization was then only four years old. At this 1949 Congress I met the founding fathers: Donald Coxeter, Ralph Jeffery, Lloyd Williams, Eric O'Connor, and others. What a fine group of fine mathematicians.

There I met the founders of the Congress and established a lasting friendship with them and others. I well remember Lloyd Williams, who raised tens of thousands of dollars from private corporations to support the work of the Congress. Also, Ralph Jeffery who started, and guided, the Summer Research Institutes in Kingston where I spent three great summers. I also started a friendship with Father O'Connor who worked tirelessly for the benefit of others. I met Donald Coxeter who played such an important role in my life.

William Moser's relations with Donald Coxeter were beyond those of a former student: during his whole life he spent many respectful hours visiting Coxeter, particularly later in Coxeter's life. Some of his trips to Toronto have been only to visit Coxeter.

When we began to consider the scope of this book, we envisaged a catalogue supplying at least one abstract definition for any finitely-generated group that the reader might propose. But we soon realized that more or less arbitrary restrictions are necessary, because interesting groups are so numerous.

... brings together a great deal of information on generators and relations for a wide variety of groups. For instance, it deals with the crystallographic groups, with the fundamental groups of surfaces, with the symmetric and related groups, with the projective linear groups over finite fields, and with groups on real Euclidean space generated by reflections. There is also a systematic method for checking the sufficiency of a set of relations, and considerable attention to graphical representations. The book will be invaluable to anyone who believes, as I do, that progress in Group Theory depends primarily on an intimate knowledge of a large number of special groups.

This paper is certain to interest a wide class of readers, because of the generality and importance of the problems considered and the elementary nature and great ingenuity of the methods used. Let there be a finite number $n ( > 1)$ of points in the real Euclidean or the real projective plane, not all on one line, and let every pair of distinct points be joined by a line. The authors consider two most interesting and general questions concerning such configurations of $n$ non-collinear points and the lines determined by them: What is the minimum number of lines determined by the $n$ points, and what is the minimum number of those lines which have the property that each of them passes through exactly two of the $n$ points?

During his 32 years in the Department of Mathematics and Statistics, Moser fashioned and taught his own geometry courses in an original manner, making collections of research problems along the way. In order to promote his specialty, Moser became involved in the teaching of high school mathematics teachers, making films about geometry, organizing mathematical competitions and collecting and disseminating competition problems.

Since the beginning of his career in 1955, William Moser has been involved with high school/college mathematics in a variety of ways, particularly serving on committees arranging provincial mathematics competitions in Saskatchewan, Manitoba and Quebec. He was a member of the CMS Education Committee when, under the chairmanship of Lloyd Dulmage, it instituted the Canadian Mathematical Olympiad. He edited (some with Ed Barbeau) the booklets containing the problems, solutions and results of the Canadian mathematical Olympiads from 1969 to 1978. During the years 1975-1985, he, E Barbeau and M S Klamkin edited five collections of problems (500 problems altogether) that the CMS printed and distributed widely. The full collection, corrected and improved, has been published by Mathematics Magazine in its spectrum series as "500 Mathematical Challenges" in 1995. He has also taught NSF Summer Institutes for High School Teachers (1959-62) and participated in the College Geometry Project (1964-68) at the University of Minnesota, making beautiful films, one about Coxeter.

As a young Master's student from Scotland attending McGill University I was introduced to the delights of computational group theory by my cigar chain-smoking supervisor William Moser. While working on my dissertation in the summer of 1965, I met up with William Moser in Minneapolis where he was heavily involved in the Minnemath project at the University of Minnesota. It gave me an opportunity to visit the Guthrie theatre in Minneapolis, encouraged by Moser who is a great enthusiast for the theatre. At a professional level my career has revolved round the Todd-Coxeter coset enumeration algorithm to which I was first introduced by Moser.

The author wishes to express deep gratitude to a scholar, Professor W O J Moser, whose ideas and encouragement made this thesis possible.

"Donald made many great contributions to mathematics. I made one great contribution," recounted Moser. Moser's opportunity came at the end of Coxeter's 1955 summer of roving lectures, after his session in Stillwater, at Oklahoma State University. Moser drove down to meet Coxeter and serve as his assistant, taking detailed notes of the well-polished lectures. "At the end of the summer we drove north, to civilisation," said Moser wryly. "We were in my car and Donald asked me if he could drive. It was a new car. Indeed it was the first car I had ever purchased, a green 1955 Plymouth 2-door. I paid $2,000 for it and drove it to Oklahoma. But I agreed. I was surprised to see that he was an aggressive driver. At one point he was trying to pass a car while driving up a hill on a 2-lane highway. I immediately perceived that this was not a prudent thing to do. He tried to coax the car to go faster but it wouldn't respond. At the last moment I shrieked at him, 'Pull back, pull back'. I was probably his only student to shriek at him. He began to pull back and at that moment a truck came over the hill. He managed to get back in the right lane just in time. I HAD SAVED HIS LIFE! And mine. But saving Coxeter's life was my greatest contribution to mathematics."

Be generous and patient as teachers, be active in projects which benefit the mathematical community and, above all, have as long and as happy a mathematical life as I have had, and am still having.