Question: What profession has both Ivan Fesenko and Mark Krein held?

Context paragraphs:
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 ().

Chartered Institute of Trade Mark Attorneys: The Chartered Institute of Trade Mark Attorneys (CITMA) was founded in 1934 as the British professional body for trade mark attorneys.  It received a Royal Charter in 2016 which saw its name change from ITMA.  CITMA is a professional membership organisation with the power to shape law and practice – nationally and internationally, as well as supporting and promoting the trade mark attorney profession.  It has legal responsibility for regulating the profession, which is delegated to the Intellectual Property Regulation Board (IPReg).

Markov–Krein theorem: In probability theory, the Markov–Krein theorem gives the best upper and lower bounds on the expected values of certain functions of a random variable where only the first moments of the random variable are known.  The result is named after Andrey Markov and Mark Krein.

Mark Krein: Mark Grigorievich Krein (Ukrainian: Марко Григорович Крейн , Russian: Марк Григо́рьевич Крейн ; 3 April 1907 – 17 October 1989) was a Soviet Jewish mathematician, one of the major figures of the Soviet school of functional analysis.  He is known for works in operator theory (in close connection with concrete problems coming from mathematical physics), the problem of moments, classical analysis and representation theory.

Ivan Fesenko: Ivan Fesenko (Russian: Иван Борисович Фесенко ; born 1962) is a mathematician working in number theory and other areas of modern mathematics.

Horace Ezra Bixby: Horace Ezra Bixby (May 8, 1826 - August 1, 1912) was a steamboat pilot on the Mississippi-Missouri-Ohio river system from the late 1840s until his death in 1912.  Bixby is notable in his own right for his high standing in his profession, for his technical contributions to it, and for his service in the American Civil War.  However, he is best known for having had as his "cub pilot" (that is, apprentice or trainee) the young man known to him as Sam Clemens, later to become famous under his pen name as American author Mark Twain.  Twain's descriptions of Bixby's character and pedagogic style form a good part of his memoir "Life on the Mississippi", and it was through this medium that Bixby—much to his annoyance—became well-known beyond the circles of his family, friends and profession.

Ivan Allen Jr. Prize for Progress and Service: Prior to the Ivan Allen Jr.  Prize for Social Courage, the Georgia Institute of Technology's Ivan Allen College of Liberal Arts had awarded the Ivan Allen Jr.  Prize for Progress & Service.  Awarded annually from 2001-2010, the Prize honored individuals who had contributed to the progress of American civilization through his or her service to a field or profession associated with the academic disciplines taught in the Ivan Allen College.

Samuel Manetoali: Samuel Manetoali (born January 24, 1969) is a member of the National Parliament of the Solomon Islands.  He represents the Gao/Bugotu constituency in Isabel Province.  He attended Lepi Primary School and then went on to do his secondary education at the prestigious King George Sixth National School in Honiara.  He attended law school at the University of Papua New Guinea and graduated with an LLB degree and further unspecified qualifications from the University of Tasmania and University of South Australia.  Prior to entering politics he worked in the country's Public Solicitors Office, then he worked as a private lawyer and a legal adviser to the Isabel Provincial Government.  He first entered parliament in the 2006 general election and re-elected in the 2010 general election. .  He served as the Solomon Islands' Minister of Police, National Security and Correctional Services in Prime Minister Derek Sikua's Cabinet until May 2009, when he was transferred to the position of Minister for Lands, Survey, and Housing.  Following the 2010 general election, he remained in Cabinet, under new Prime Minister Danny Philip, as Minister for Tourism and Culture.  In this year's (2014) general election which was held on the 19th November, he was voted in again for the third term with a landslide victory.  .  He contested as an independent candidate in last week's election. .  As a lawyer, many people had expected more from him seeing that many world leaders including Barack Obama and Tony Abott are lawyers by profession and he appears to be a potential candidate for the prime minister's post given his experience as a politician (3 terms including the current term) and his noble profession.  His current success in the recent election could be attributed to projects such as mini-fisheries projects that he established in the various villages in his constituency.  He also helped the villages and communities by giving handouts such as roofing irons, outboard motor engines, fiber boats, solar panels, cash money and other form of support as a way to maintain and broaden his support.  He also supported local tourism in his constituency by giving financial help to tourism operators such as on Sigana Island,albeit, tourism is still at its infant stage in his constituency.  His other elixir to maintain his popularity and support is through facilitating and sending Bamboo Bands/groups notably the Hageulu bamboo band overseas for the promotion of tourism and culture for the country and he managed to do that in his capacity as the minister of Tourism and Culture in the Lilo-led government.  He was also instrumental in establishing the Gao-Bugotu Cultural Festival initially held in Huali Village in Gao and in Sepi/Lepi Villages in Bugotu.

Tannaka–Krein duality: 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".

Ivan Vasilievich: Back to the Future: Ivan Vasilievich Changes Profession (Russian: Иван Васильевич меняет профессию , "Ivan Vasilyevich menyayet professiyu " ) is a Soviet comic science fiction film directed by Leonid Gaidai in 1973.  In the United States the film has sometimes been sold under the title Ivan Vasilievich: Back to the Future.  This film is based on the play "" by Mikhail Bulgakov and was one of the most attended movies in the Soviet Union in 1973 with more than 60 million tickets sold.

Supporting paragraphs: Mark Krein Ivan Fesenko
Answer: mathematician