Question: Lazar Lyusternik and Israel Gelfand, have which mutual occupation?
Context: Sparse grids are numerical techniques to represent, integrate or interpolate high dimensional functions.  They were originally developed by the Russian mathematician Sergey A. Smolyak, a student of Lazar Lyusternik, and are based on a sparse tensor product construction.  Computer algorithms for efficient implementations of such grids were later developed by Michael Griebel and Christoph Zenger. Lazar Aronovich Lyusternik (also Lusternik, Lusternick, Ljusternik; Ла́зарь Аро́нович Люсте́рник ; 31 December 1899, Zduńska Wola, Congress Poland, Russian Empire (present-day Republic of Poland) – 23 July 1981, Moscow, Russia, Soviet Union) was a Soviet mathematician. In operator theory, the Gelfand–Mazur theorem is a theorem named after Israel Gelfand and Stanisław Mazur which states that a Banach algebra with unit over the complex numbers in which every nonzero element is invertible is isometrically isomorphic to the complex numbers, i. e., the only complex Banach algebra that is a division algebra is the complex numbers C. In mathematics, the Gelfand–Naimark theorem states that an arbitrary C*-algebra "A" is isometrically *-isomorphic to a C*-algebra of bounded operators on a Hilbert space.  This result was proven by Israel Gelfand and Mark Naimark in 1943 and was a significant point in the development of the theory of C*-algebras since it established the possibility of considering a C*-algebra as an abstract algebraic entity without reference to particular realizations as an operator algebra. Samson Lulievich Shatashvili (Georgian: სამსონი შათაშვილი, Russian: Самсон Лулиевич Шаташвили) is a theoretical and mathematical physicist who has been working at Trinity College Dublin, Ireland, since 2002.  He holds the University Chair of Natural Philosophy (1847) and is the director of the Hamilton Mathematical Institute.  He is also affiliated with the Institut des Hautes Études Scientifiques (IHÉS), where he held the Louis Michel Chair from 2003 to 2013 and currently holds the Israel Gelfand Chair.  Prior to moving to Trinity College, he was a professor of physics at Yale University from 1994. In mathematics, Liouville–Bratu–Gelfand equation or Lioville's equation is a non-linear eigenvalue Poisson equation, named after the mathematicians Joseph Liouville, G. Bratu and Israel Gelfand.  The equation reads In functional analysis, a discipline within mathematics, given a C*-algebra "A", the Gelfand–Naimark–Segal construction establishes a correspondence between cyclic *-representations of "A" and certain linear functionals on "A" (called "states").  The correspondence is shown by an explicit construction of the *-representation from the state.  It is named for Israel Gelfand, Mark Naimark, and Irving Segal. Victor Borisovich Lidskii (Russian: Виктор Борисович Лидский , 4 May 1924, Odessa – 29 July 2008, Moscow) was a Soviet and Ukrainian mathematician who worked in spectral theory, operator theory, and shell theory.  Lidskii discovered the Lidskii theorem in 1959.  His adviser at Moscow State University was Israel Gelfand. Israel Moiseevich Gelfand, also written Israïl Moyseyovich Gel'fand, or Izrail M. Gelfand (Yiddish: ישראל געלפֿאַנד‎ , Russian: Изра́иль Моисе́евич Гельфа́нд ; 2 September [O.S. 20 August] 1913 – 5 October 2009) was a prominent Soviet mathematician.  He made significant contributions to many branches of mathematics, including group theory, representation theory and functional analysis.  The recipient of many awards, including the Order of Lenin and the Wolf Prize, he was a Fellow of the Royal Society and professor at Moscow State University and, after immigrating to the United States shortly before his 76th birthday, at Rutgers University. Vladimir Gilelevich Maz'ya (Russian: Владимир Гилелевич Мазья ; born December 31, 1937) (the family name is sometimes transliterated as Mazya, Maz'ja or Mazja) is a Russian-born Swedish mathematician, hailed as "one of the most distinguished analysts of our time" and as "an outstanding mathematician of worldwide reputation", who strongly influenced the development of mathematical analysis and the theory of partial differential equations.  His early achievements include: his work on Sobolev spaces, in particular the discovery of the equivalence between Sobolev and isoperimetric/isocapacitary inequalities (1960), his counterexamples related to Hilbert's 19th and Hilbert's 20th problem (1968), his solution, together with Yuri Burago, of a problem in harmonic potential theory (1967) posed by , his extension of the Wiener regularity test to p –Laplacian and the proof of its sufficiency for the boundary regularity.  Maz'ya solved V. Arnol'd's problem for the oblique derivative boundary value problem (1970) and F. John's problem on the oscillations of a fluid in the presence of an immersed body (1977).  In recent years, he proved a Wiener's type criterion for higher order elliptic equations, together with M. Shubin solved a problem in the spectral theory of the Schrödinger operator formulated by Israel Gelfand in 1953, found necessary and sufficient conditions for the validity of maximum principles for elliptic and parabolic systems of PDEs and introduced the so–called approximate approximations.  He also contributed to the development of the theory of capacities, nonlinear potential theory, the asymptotic and qualitative theory of arbitrary order elliptic equations, the theory of ill-posed problems, the theory of boundary value problems in domains with piecewise smooth boundary.
Answer: mathematician