It is my pleasure to present the report of the Thomas Stieltjes Institute for Mathematics on the years 1998 and 1999. After the report on the single year 1997, the tradition of biennial reports is resumed. The report covers the end of the first five year period as a research school and the start of the second. On June 4, 1999, the recognition of the Stieltjes Institute as a research school was renewed by the Royal Netherlands Academy for Arts and Sciences for another five years. In the motivation the quality of the research groups was characterised as good to excellent. In the new period there are some changes in the research groups. Because of its participation in an other research school the group Theoretical Computer Science left the Stieltjes Institute. On the other hand, the Analysis group of the Eindhoven University of Technology joined the Stieltjes Institute. Leiden University continued to be the administrator of the Institute.
During the past two years we have continued to care about the quality of the research and of the graduate study. Apart from the regular evaluation of the research by the scientific committee, which resulted in some measures by the board, there were various positive actions. In 1999 Professor J.A. Wellner from the University of Washington in Seattle, USA, was the first Stieltjes Visiting Professor. In 1999 J.A. van Hamel received the Stieltjes Prize for the best thesis in 1997 and J.V. Stokman for the best one in 1998. Apart from the regular seminars and workshops about a special topic in mathematics we started with some Stieltjes Afternoons at which lectures were given for all members of the Stieltjes Institute. In this and other ways the collaboration of Stieltjes members was enhanced. A new initiative is the organisation of Stieltjes Weeks starting in 2000. Researchers from different universities will lecture and work intensively with (advanced under)graduate students from all Stieltjes universities on a topic which has broad interest.
The quality of Stieltjes members was recognised in various ways. H.W. Lenstra was the first mathematician to receive the prestigious Spinoza grant from the Netherlands Organization for Scientific Research (NWO). This will enable him to build a strong number theory group around him. In 1998 S.M. Verduyn Lunel and in 1999 another member of the Stieltjes Institute, E.M. Opdam, received Pioneer grants from NWO. An honorary doctorate was awarded to R. Tijdeman by the University of Debrecen, Hungary.
The cooperation with other research schools was strengthened. With MRI and EIDMA an application was initiated for the depth strategy of NWO. Afterwards informal discussions started which may lead to a national research school committee for mathematics. In accordance with proposals in a report of the Advisory Committee for Science and Technology (AWT) of the Ministry of Education, Culture and Science, the Stieltjes Institute stimulated the cooperation and coordination of teaching of mathematics students at undergraduate level by universities participating in the Stieltjes Institute.
Finally, the person who led the Stieltjes from the beginning, W.R. van Zwet retired from the university and passed on the directorship. In March 1999, a successful symposium was held on the State of the Art in Probability and Statistics, concluded by the last official lecture by Van Zwet at Leiden University. He remained director until July 1999. On behalf of the Stieltjes Institute I want to thank him here for all the good things he has done for the institute. We are still not without his good advice, for at present he attends the meetings of the Board of the Stieltjes Institute as director of the associated European research institute EURANDOM.