Question: Nikolai Chebotaryov and Dmitri Egorov, have which occupation?

Context paragraphs:
Egorov's theorem: In measure theory, an area of mathematics, Egorov's theorem establishes a condition for the uniform convergence of a pointwise convergent sequence of measurable functions.  It is also named Severini–Egoroff theorem or Severini–Egorov theorem, after Carlo Severini, an Italian mathematician, and Dmitri Egorov, a Russian physicist and geometer, who published independent proofs respectively in 1910 and 1911.

Felix Gantmacher: Felix Ruvimovich Gantmacher (Russian: Феликс Рувимович Гантмахер ) (23 February 1908 – 16 May 1964) was a Soviet mathematician, professor at Moscow Institute of Physics and Technology, well known for his contributions in mechanics, linear algebra and Lie group theory.  In 1925–1926 he participated in seminar guided by Nikolai Chebotaryov in Odessa and wrote his first research paper in 1926.

Dmitri Egorov: Dmitri Fyodorovich Egorov (Russian: Дми́трий Фёдорович Его́ров ; December 22, 1869 – September 10, 1931) was a Russian and Soviet mathematician known for significant contributions to the areas of differential geometry and mathematical analysis.  He was President of the Moscow Mathematical Society (1923 — 1930).

Matematicheskii Sbornik: Matematicheskii Sbornik (Russian: Математический сборник , abbreviated "Mat.  Sb.")  is a peer reviewed Russian mathematical journal founded by the Moscow Mathematical Society in 1866.  It is the oldest successful Russian mathematical journal.  The English translation is "Sbornik: Mathematics".  It is also sometimes cited under the alternative name "Izdavaemyi Moskovskim Matematicheskim Obshchestvom" or its French translation "Recueil mathématique de la Société mathématique de Moscou", but the name "Recueil mathématique" is also used for an unrelated journal, "Mathesis".  Yet another name, "Sovetskii Matematiceskii Sbornik", was listed in a statement in the journal in 1931 apologizing for the former editorship of Dmitri Egorov, who had been recently discredited for his religious views; however, this name was never actually used by the journal.

Nikolai Chebotaryov: Nikolai Grigorievich Chebotaryov (often spelled Chebotarov or Chebotarev, Russian: Никола́й Григо́рьевич Чеботарёв , Ukrainian: Микола Григорович Чоботарьов ) (15 June [O.S. 3 June] 1894 – 2 July 1947) was a noted Ukrainian and Soviet mathematician.  He is best known for the Chebotaryov density theorem.

Symphony No. 1 (Shostakovich): The Symphony No. 1 in F minor (Opus 10) by Dmitri Shostakovich was written in 1924–1925, and first performed in Leningrad by the Leningrad Philharmonic under Nikolai Malko on 12 May 1926.  Shostakovich wrote the work as his graduation piece at the Petrograd Conservatory, completing it at the age of 18.

Chebotarev's density theorem: Chebotarev's density theorem in algebraic number theory describes statistically the splitting of primes in a given Galois extension "K" of the field formula_1 of rational numbers. Generally speaking, a prime integer will factor into several ideal primes in the ring of algebraic integers of "K".  There are only finitely many patterns of splitting that may occur.  Although the full description of the splitting of every prime "p" in a general Galois extension is a major unsolved problem, the Chebotarev density theorem says that the frequency of the occurrence of a given pattern, for all primes "p" less than a large integer "N", tends to a certain limit as "N" goes to infinity.  It was proven by Nikolai Chebotaryov in his thesis in 1922, published in .

Symphony No. 2 (Shostakovich): Dmitri Shostakovich wrote his Symphony No. 2 in B major, Op. 14 and subtitled "To October", for the 10th anniversary of the October Revolution.  It was first performed by the Leningrad Philharmonic Orchestra and the Academy Capella Choir under Nikolai Malko, on 5 November 1927.  After the premiere, Shostakovich made some revisions to the score, and this final version was first played in Moscow later in 1927 under the baton of Konstantin Saradzhev.  It was also the first time any version of the work had been played in Moscow.

Association for Contemporary Music: Association for Contemporary Music (ACM) (Russian: ACM - Ассоциация Современной Музыки , "ASM - Assotsiatsiya Sovremennoy Muzyki") was an alternative organization of Russian composers interested in avant-garde music.  It was founded by Nikolai Roslavets in 1923.  ACM ran concert series and published magazines promoting the modernist music of Mahler, Schoenberg, Berg, Webern, Krenek, and Hindemith, as well as the work of its members.  Its leading members were Dmitri Shostakovich, Nikolai Myaskovsky, Vissarion Shebalin, Alexander Mosolov, Gavriil Popov, and Vladimir Shcherbachev.  The organization's enthusiasm for avant-garde Western music and for experimentation met with opposition from the Russian Association of Proletarian Musicians (RAPM), which by the late 1920s had eclipsed the ACM in terms of cultural influence.  Both organizations existed until 23 April 1932, when they were abolished by the Decree on the Reformation of Literary and Artistic Organizations.

Carlo Severini: Carlo Severini (10 March 1872 – 11 May 1951) was an Italian mathematician: he was born in Arcevia (Province of Ancona) and died in Pesaro.  Severini, independently from Dmitri Fyodorovich Egorov, proved and published earlier a proof of the theorem now known as Egorov's theorem.

Supporting paragraphs: Nikolai Chebotaryov Dmitri Egorov
Answer: mathematician