Keres was a three-time schoolboy champion of the country, in 1930, 1932, and 1933. His playing matured after playing correspondence chess extensively while in high school. He probably played about 500 correspondence games, and at one stage had 150 correspondence games going simultaneously. In 1935, he won the Internationaler Fernschachbund (IFSB) international correspondence chess championship. From 1937 to 1941 he studied mathematics at the University of Tartu, and competed in several interuniversity matches.Grandmaster of Chess: The Complete Games of Paul Keres, by Paul Keres, edited and translated by Harry Golombek, Arco, New York, 1977
