Question: Which Russian mathmatician contributed to number theory, Grigori Perelman or Ivan Fesenko?

full_context: Document 1: Manifold Destiny: "Manifold Destiny" is an article in "The New Yorker" written by Sylvia Nasar and David Gruber and published in the August 28, 2006 issue of the magazine. It claims to give a detailed account (including interviews with many mathematicians) of some of the circumstances surrounding the proof of the Poincaré conjecture, one of the most important accomplishments of 20th and 21st century mathematics, and traces the attempts by three teams of mathematicians to verify the proof given by Grigori Perelman.
Document 2: Ivan Fesenko: Ivan Fesenko (Russian: Иван Борисович Фесенко ; born 1962) is a mathematician working in number theory and other areas of modern mathematics.
Document 3: Victor Kolyvagin: Victor Alexandrovich Kolyvagin (Russian: Ви́ктор Алекса́ндрович Колыва́гин ) is a Russian mathematician who wrote a series of papers on Euler systems, leading to breakthroughs on the Birch and Swinnerton-Dyer conjecture, and Iwasawa's conjecture for cyclotomic fields. His work also influenced Andrew Wiles's work on Fermat's Last Theorem.
Document 4: Serhiy Fesenko: Sergey Fesenko Jr. (also spelled as Sergiy or Serhiy, born June 5, 1982) is a long-distance freestyle swimmer from Ukraine. He competed in the 2000 Olympic Games in Sydney, Australia, 2004 Olympic Games in Athens, Greece and qualified to represent his country at the 2008 Olympic Games in Beijing, China. As a student at Indiana University, Fesenko was Big Ten swimmer of the week twice and NCAA swimmer of the week once in the 2005–2006 collegiate season. His father, Sergey Fesenko, Sr., won the gold medal in the 200m butterfly at the 1980 Olympic Games in Moscow.
Document 5: Ivan Ivanov (mathematician): Ivan Ivanovich Ivanov (Russian: Иван Иванович Иванов ; 11 August 1862 – 17 December 1939) was a Russian-Soviet mathematician who worked in the field of number theory. Together with Georgy Voronoy he continued Pafnuty Chebyshev's work on the subject.
Document 6: Margulis lemma: In differential geometry, a subfield of mathematics, the Margulis lemma (named after Grigory Margulis) is a result about discrete subgroups of isometries of a non-positively curved Riemannian manifolds (e.g. the hyperbolic n-space). Roughly, it states that within a fixed radius, usually called the Margulis constant, the structure of the orbits of such a group cannot be too complicated. More precisely, within this radius around a point all points in its orbit are in fact in the orbit of a nilpotent subgroup (in fact a bounded finite number of such).
Document 7: Ivan Vinogradov: Ivan Matveevich Vinogradov {'1': ", '2': ", '3': 'ForMemRS', '4': "} (Russian: Ива́н Матве́евич Виногра́дов ; ] ; 14 September 1891 – 20 March 1983) (not to be confused with Askold Ivanovich Vinogradov of the Bombieri-Vinogradov theorem) was a Soviet mathematician, who was one of the creators of modern analytic number theory, and also a dominant figure in mathematics in the USSR. He was born in the Velikiye Luki district, Pskov Oblast. He graduated from the University of St. Petersburg, where in 1920 he became a Professor. From 1934 he was a Director of the Steklov Institute of Mathematics, a position he held for the rest of his life, except for the five-year period (1941–1946) when the institute was directed by Academician Sergei Sobolev. In 1941 he was awarded the Stalin Prize. In 1951 he became a foreign member of the Polish Academy of Sciences and Letters in Kraków.
Document 8: Nicolai Reshetikhin: Nicolai Yuryevich Reshetikhin (Russian: Николай Юрьевич Решетихин , born October 10, 1958 in Leningrad, Soviet Union) is a mathematical physicist, currently a professor of mathematics at the University of California, Berkeley and a professor of mathematical physics at the University of Amsterdam. His research is in the fields of low-dimensional topology, representation theory, and quantum groups. His major contributions are in the theory of quantum integrable systems, in representation theory of quantum groups
Document 9: Soul theorem: In mathematics, the soul theorem is a theorem of Riemannian geometry that largely reduces the study of complete manifolds of non-negative sectional curvature to that of the compact case. Cheeger and Gromoll proved the theorem in 1972 by generalizing a 1969 result of Gromoll and Wolfgang Meyer. The related soul conjecture was formulated by Gromoll and Cheeger in 1972 and proved by Grigori Perelman in 1994 with an astonishingly concise proof.
Document 10: Calabi conjecture: In mathematics, the Calabi conjecture was a conjecture about the existence of certain "nice" Riemannian metrics on certain complex manifolds, made by and proved by . Yau received the Fields Medal in 1982 in part for this proof.
Document 11: Fesenko group: In mathematics, Fesenko groups are certain subgroups of the wild automorphism groups of local fields of positive characteristic (i.e. the Nottingham group), studied by Ivan Fesenko ().
Document 12: Grigori Perelman: Grigori Yakovlevich Perelman (Russian: Григо́рий Я́ковлевич Перельма́н ; ] ; born 13 June 1966) is a Russian mathematician. He made a contribution to Riemannian geometry and geometric topology.
Document 13: Grigory Margulis: Gregori Aleksandrovich Margulis (Russian: Григо́рий Алекса́ндрович Маргу́лис , first name often given as Gregory, Grigori or Grigory; born February 24, 1946) is a Russian-American mathematician known for his work on lattices in Lie groups, and the introduction of methods from ergodic theory into diophantine approximation. He was awarded a Fields Medal in 1978 and a Wolf Prize in Mathematics in 2005, becoming the seventh mathematician to receive both prizes. In 1991, he joined the faculty of Yale University, where he is currently the Erastus L. De Forest Professor of Mathematics.
Document 14: Vladimir Voevodsky: Vladimir Alexandrovich Voevodsky ( ; Russian: Влади́мир Алекса́ндрович Воево́дский , 4 June 1966 - 30 September 2017) was a Russian mathematician. His work in developing a homotopy theory for algebraic varieties and formulating motivic cohomology led to the award of a Fields Medal in 2002. He is also known for the proof of the Milnor conjecture and motivic Bloch-Kato conjectures and for the univalent foundations of mathematics and homotopy type theory.
Document 15: Mikhail Leonidovich Gromov: Mikhail Leonidovich Gromov (also Mikhael Gromov, Michael Gromov or Mischa Gromov; Russian: Михаи́л Леони́дович Гро́мов ; born 23 December 1943), is a French-Russian mathematician known for work in geometry, analysis and group theory. He is a permanent member of IHÉS in France and a Professor of Mathematics at New York University.
ground_truth: Ivan Fesenko