Complex sentence: In 1959 Kostrikin achieved important results on Burnside's problem adn a year later, in 1960, he earned Doctor of Sciences degree and since 1963 worked at the faculty (professor since 1976).
Split into simpler sentences: In 1959 Kostrikin achieved important results on Burnside's problem. A year later he earned Doctor of Sciences degree and since 1963 worked at the faculty (professor since 1976).