 Sosonko legally emigrated from the Soviet Union to the Netherlands via Israel in 1972.He won the Dutch Championship in 1973 and 1978 (jointly).His tournament record includes 1st at Wijk aan Zee 1977, 1st at Nijmegen 1978, 3rd at Amsterdam 1980, 1st at Wijk aan Zee 1981, 3rd at Tilburg 1982 and 4th at Haninge 1988.