Complex sentence: He lived in one of the most difficult periods of contemporary Russian history: the state of mathematical sciences during this period is well described by: marxist ideology rise in the USSR universities and Academia was one of the main themes of that period.
Split into simpler sentences: He lived in one of the most difficult periods of contemporary Russian history. The state of mathematical sciences during this period is well described by: marxist ideology rise in the USSR universities and Academia was one of the main themes of that period.