The twentieth century has been one of great international conflict, but also one of increasing globalization and cooperation among nations. The history of international mathematical cooperation over the last hundred years--from the first international congress in 1897 to plans for the World Mathematical Year 2000--as told by Professor Olli Lehto, is a surprisingly compelling story. For reflected in the history of the International Mathematical Union (IMU) is all the strife among world powers, as well as aspirations for cooperation among nations in an increasingly interdependent world. The IMU, founded in the aftermath of World War I, for fifteen years excluded Germany and the other defeated Central Powers. But in the 1920s the IMU embraced principles of political neutrality, inviting every national mathematical organization to join the IMU, and this principle of nondiscrimination, while sometimes sorely tried, has held the IMU in good stead. Then came the Second World War, and again international cooperation was threatened. After World War II, a number of issues--the Cold War, the conflict between the People's Republic of China and Taiwan, a divided Germany, problems in the emerging nations of Africa--at times led to attempts to influence the IMU Executive Committee in its decisions regarding membership, location of international congresses, committee assignments, handling of protests, and awarding the coveted Fields Medals. Throughout the tumultuous past half century the IMU has sponsored International Congresses throughout the world, and Mathematics Without Borders will fill you in on all the mathematical and organizational details. But what keeps you turning pages is the very humanstory of individuals, among them many of the great mathematicians of our

At its meeting in April 1990 at the University of Cambridge, the Executive Committee of the International Mathematical Union (IMU) decided that the largely unorganized archives of the Union should be properly arranged and catalogued. Simultaneously, the Executive Committee expressed the wish that a history of the Union should be written [1). As Secretary of the Union, I had proposed that these issues be dis cussed at the Cambridge meeting, but without having had in mind any personal role in the practical execution of such projects. At that time, the papers of the IMU were stored in Zurich, at the Eidgenossische Technische Hochschule, and I saw no reason why they could not remain there. At about this time, Professor K. Chandrasekharan produced a handwritten article titled "The Prehistory of the International Mathematical Union" [2), and it seemed to me that this might serve as the beginning of a more compre hensive history. I had first thought that Tuulikki MakeUiinen, who during eight years as the Office Secretary ofthe IMU had become well acquainted with the Union, would do the arranging of the archives in Zurich. She had a preliminary look at the material there, but it soon became clear that the amount of work required to bring order to it was too great to be accomplished in a few short visits from Helsinki. The total volume of material was formidable.

The present text is a fairly direct translation of the German edition "Quasikonforme Abbildungen" published in 1965. During the past decade the theory of quasi conformal mappings in the plane has remained relatively stable. We felt, therefore, that major changes were not necessarily required in the text. In view of the recent progress in the higher-dimensional theory we found it preferable to indicate the two-dimensional case in the title. Our sincere thanks are due to K. W. Lucas, who did the major part of the translation work. In shaping the final form of the text with him we received many valuable suggestions from A. J. Lohwater. We are indebted to Anja Aaltonen and Pentti Dyyster for the prepara- tion of the manuscript, and to Timo Erkama and Tuomas Sorvali for the careful reading and correction of the proofs. Finally, we should like to express our thanks to Springer-Verlag for their friendly coopera- tion in the production of this volume.