Given the question: Information: - Nikolai Vladimirovich Efimov ( Russian : ; 31 May 1910 in Orenburg -- 16 October 1982 in Moscow ) was a Soviet mathematician . He is most famous for his work on generalized Hilbert 's problem on surfaces of negative curvature . Efimov grew up in Rostov - on - Don and graduated from Rostov State University , where he studied with Morduhai - Boltovskoi . He worked at Voronezh State University from 1934 to 1941 . He taught at the Moscow State University since 1946 . Aleksei Pogorelov was one of his students there . He received the Lobachevsky Medal in 1951 and Lenin Prize in 1966 . He was an invited plenary speaker at the International Congress of Mathematicians in Moscow , 1966 . He became a corresponding member of the Soviet Academy of Sciences in 1979 . - Moscow (or ) is the capital and most populous city of Russia, with 12.2 million residents within the city limits and 16.8 million within the urban area. Moscow has the status of a Russian federal city. - A mathematical problem is a problem that is amenable to being represented, analyzed, and possibly solved, with the methods of mathematics. This can be a real-world problem, such as computing the orbits of the planets in the solar system, or a problem of a more abstract nature, such as Hilbert's problems.<br> It can also be a problem referring to the nature of mathematics itself, such as Russell's Paradox. - Russia (from the Rus'), also officially known as the Russian Federation, is a country in Eurasia. At , Russia is the largest country in the world by surface area, covering more than one-eighth of the Earth's inhabited land area, and the ninth most populous, with over 140million people at the end of March 2016. The European western part of the country is much more populated and urbanised than the eastern, about 77% of the population live in European Russia. Russia's capital Moscow is one of the largest cities in the world, other major urban centers include Saint Petersburg, Novosibirsk, Yekaterinburg, Nizhny Novgorod and Samara. - Kazakhstan ( "Qazaqstan", "Kazakhstan"), officially the Republic of Kazakhstan ("Qazaqstan Respwblikas" "Respublika Kazakhstan"), is a transcontinental country in northern Central Asia and Eastern Europe. Kazakhstan is the world's largest landlocked country, and the ninth largest in the world, with an area of . Kazakhstan is the dominant nation of Central Asia economically, generating 60% of the region's GDP, primarily through its oil/gas industry. It also has vast mineral resources. - In differential geometry, a (smooth) Riemannian manifold or (smooth) Riemannian space ("M","g") is a real smooth manifold "M" equipped with an inner product formula_1 on the tangent space formula_2 at each point formula_3 that varies smoothly from point to point in the sense that if "X" and "Y" are vector fields on "M", then formula_4 is a smooth function. The family formula_1 of inner products is called a Riemannian metric (tensor). These terms are named after the German mathematician Bernhard Riemann. The study of Riemannian manifolds constitutes the subject called Riemannian geometry. - Orenburg Oblast ("Orenburgskaya oblast") is a federal subject of Russia (an oblast). Its administrative center is the city of Orenburg. From 1938 to 1957, it bore the name "Chkalov Oblast" in honor of Valery Chkalov. Population: 2,033,072 (2010 Census). Geography. The most important river of the oblast is the Ural. - An urban area is a human settlement with high population density and infrastructure of built environment. Urban areas are created through urbanization and are categorized by urban morphology as cities, towns, conurbations or suburbs. In urbanism, the term contrasts to rural areas such as villages and hamlets and in urban sociology or urban anthropology it contrasts with natural environment. The creation of early predecessors of urban areas during the urban revolution led to the creation of human civilization with modern urban planning, which along with other human activities such as exploitation of natural resources leads to human impact on the environment. - Mathematics (from Greek "mathma", knowledge, study, learning) is the study of topics such as quantity (numbers), structure, space, and change. There is a range of views among mathematicians and philosophers as to the exact scope and definition of mathematics. - In mathematics, a curve (also called a curved line in older texts) is, generally speaking, an object similar to a line but that need not be straight. Thus, a curve is a generalization of a line, in that curvature is not necessarily zero. - Orenburg is the administrative center of Orenburg Oblast (region), Russia, lies on the River Ural, southeast of Moscow. Its geographical location is in the boundary of Europe and Asia. Orenburg is also very close to the border with Kazakhstan. Population: 548,331 (2010 Census); 549,361 (2002 Census); - A mathematician is someone who uses an extensive knowledge of mathematics in his/her work, typically to solve mathematical problems. - In geometry, Euclidean space encompasses the two-dimensional Euclidean plane, the three-dimensional space of Euclidean geometry, and certain other spaces. It is named after the Ancient Greek mathematician Euclid of Alexandria. The term "Euclidean" distinguishes these spaces from other types of spaces considered in modern geometry. Euclidean spaces also generalize to higher dimensions. - A circle is a simple closed shape in Euclidean geometry. It is the set of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant. The distance between any of the points and the centre is called the radius. - In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is the length of any of them. The name comes from Latin "r""adius", meaning "ray" but also the spoke of a chariot wheel. The plural of "radius" can be either "radii" (from the Latin plural) or the conventional English plural "radiuses". The typical abbreviation and mathematic variable name for "radius" is r. By extension, the diameter d is defined as twice the radius: - The Kazakhs (also spelled Kazaks, Qazaqs , , ; the English name is transliterated from Russian) are a Turkic people who mainly inhabit the southern part of Eastern Europe Ural mountains and northern parts of Central Asia (largely Kazakhstan, but also found in parts of Uzbekistan, China, Russia and Mongolia), the region also known as Eurasian sub-continent. Kazakh identity is of medieval origin and was strongly shaped by the foundation of the Kazakh Khanate between 1456 and 1465, when several tribes under the rule of the sultans Zhanibek and Kerey departed from the Khanate of Abu'l-Khayr Khan. - In mathematics, curvature is any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object such as a surface deviates from being a "flat" plane, or a curve from being "straight" as in the case of a line, but this is defined in different ways depending on the context. There is a key distinction between "extrinsic curvature", which is defined for objects embedded in another space (usually a Euclidean space) in a way that relates to the radius of curvature of circles that touch the object and "intrinsic curvature", which is defined in terms of the lengths of curves within a Riemannian manifold. Given the information, choose the subject and object entities that have the relation of 'field of work'.
The answer is:
nikolai efimov , differential geometry