At birthday parties the young boy saw teachers all the time.

I remember the hard problems in applied arithmetic, about rowing boats in a flowing river.

Jaap at once became a member of the little club of Leiden mathematics students living in The Hague, gathering weekly, usually at my home. ... Jaap was much more social than the others, certainly much more social than I was, and it always remained like that. At an early age already, Jaap had experience in what is now called Networking.

This thesis contains the proofs promised in a recent note that the congruence order of the elliptic plane, with respect to the class of metric spaces, is seven (that is, seven is the smallest number with the property that an arbitrary metric space is congruent with a subset of the elliptic plane whenever each seven of its points are). Though the algebraic-geometric methods by which this result is established occasionally lead to proofs involving the examination of many cases and subcases (the longest proof covers more than seven pages) and they could hardly be carried through in elliptic three-space, the arguments (elementary in character) are presented in a clear and orderly manner. The reader must be referred to this painstaking work itself for details.

Jaap organized the mathematical department and the mathematical curricula all by himself. It was really a one-man-show. He was a wonderful organizer, knew to attract quite a good group of professors and instructors, and he let them do it the way he wanted it to do.

It is remarkable, for a mathematician, that Seidel's third period, as a prominent scientist, started when he was already 47 years old. The joint paper with Van Lint in 1966 (still cited) started a long sequence of important contributions to the theory of strongly regular graphs and design theory. He never ceased being a geometer, but algebraic methods and tools from algebra influenced his work increasingly. This algebraic trend and the fact that he is not a soloist, but the epitome of a collaborator, led to numerous joint papers with P J Cameron, Ph Delsarte, and J-M Goethals. A continued interest in very many other parts of mathematics was rewarded: a number of papers linked his own research to other areas such as group theory and the theory of integration.

Jaap Seidel loved Mathematics. He wanted to learn it, to understand it, and most of all to teach it. In his courses and personal contacts he was very inspiring. Many mathematicians, especially young ones, were influenced by Jaap. Besides being a teacher, he was also very interested in what other researchers were doing. He always tried to find links to subjects he had been working on. Jaap's work makes connections with several branches in mathematics, and he had struck friendships with mathematicians all over the world. He has been called an ambassador of mathematics.

Professor Seidel's love of mathematics and his enthusiasm as an expositor of mathematics have led to an international reputation as an ambassador of mathematics. He has been especially active in Eastern Europe and in Asia where he has contacted many mathematicians and introduced their work to the Western world. His encouragement and enthusiasm have been especially valuable to young mathematicians. Many of us have been warmly welcomed by Jaap and Ada into their home and into their family. Very quickly, mutual mathematical interests grew into a close personal friendship.