Career
Sosonko moved from the Soviet Union to the Netherlands via Israel in 1972. This was a highly publicised defection, which led to the Union of the Soviet Socialist Republics Chess Federation pressuring FIDE to declare him an "unperson". 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.
He also drew a match with January Timman (+1 =0 −1) in 1984.
Sosonko played for the Dutch team at the Chess Olympiads eleven times, in 1974-1984, and 1988-1996.