question: What was the occupation of both Lev Pontryagin and Vladimir Drinfeld?
answer: mathematician
context: Title: Vladimir Drinfeld
  Passage: Vladimir Gershonovich Drinfeld (Russian: Влади́мир Гершо́нович Дри́нфельд ; born February 14, 1954), surname also romanized as Drinfel'd, is a Ukrainian mathematician currently working at the University of Chicago.
  Title: Andronov–Pontryagin criterion
  Passage: The Andronov–Pontryagin criterion is a necessary and sufficient condition for the stability of dynamical systems in the plane.  It was derived by Aleksandr Andronov and Lev Pontryagin in 1937.
  Title: Lev Pontryagin
  Passage: Lev Semyonovich Pontryagin (Russian: Лев Семёнович Понтрягин , also written Pontriagin or Pontrjagin) (3 September 1908 – 3 May 1988) was a Soviet mathematician.  He was born in Moscow and lost his eyesight due to a primus stove explosion when he was 14.  Despite his blindness he was able to become one of the greatest mathematicians of the 20th century, partially with the help of his mother Tatyana Andreevna who read mathematical books and papers (notably those of Heinz Hopf, J. H. C. Whitehead, and Hassler Whitney) to him.  He made major discoveries in a number of fields of mathematics, including algebraic topology and differential topology.
  Title: Tannaka–Krein duality
  Passage: In mathematics, Tannaka–Krein duality theory concerns the interaction of a compact topological group and its category of linear representations.  It is a natural extension of Pontryagin duality, between compact and discrete commutative topological groups, to groups that are compact but noncommutative.  The theory is named for two men, the Soviet mathematician Mark Grigorievich Krein, and the Japanese Tadao Tannaka.  In contrast to the case of commutative groups considered by Lev Pontryagin, the notion dual to a noncommutative compact group is not a group, but a category Π("G") with some additional structures, formed by the finite-dimensional representations of "G".
  Title: Alexander duality
  Passage: In mathematics, Alexander duality refers to a duality theory presaged by a result of 1915 by J. W. Alexander, and subsequently further developed, particularly by P. S. Alexandrov and Lev Pontryagin.  It applies to the homology theory properties of the complement of a subspace "X" in Euclidean space, a sphere, or other manifold.  It is generalized by Spanier-Whitehead duality.
citations: Lev Pontryagin Vladimir Drinfeld