Were Mark Krein and Lev Pontryagin from the same country?
Lev Pontryagin: Lev Semyonovich Pontryagin (Russian: Лев Семёнович Понтрягин , also written Pontriagin or Pontrjagin) (3 September 1908 – 3 May 1988) was a Soviet mathematician.
i don't know