In mathematics, Ratner's theorems are a group of major theorems in ergodic theory concerning unipotent flows on homogeneous spaces proved by Marina Ratner around 1990.
 The theorems grew out of Ratner's earlier work on horocycle flows.
 The study of the dynamics of unipotent flows played a decisive role in the proof of the Oppenheim conjecture by Grigory Margulis.
 Ratner's theorems have guided key advances in the understanding of the dynamics of unipotent flows.
 Their later generalizations provide ways to both sharpen the results and extend the theory to the setting of arbitrary semisimple algebraic groups over a local field.
In mathematics, the multiplicative ergodic theorem, or Oseledets theorem provides the theoretical background for computation of Lyapunov exponents of a nonlinear dynamical system.
 It was proved by Valery Oseledets (also spelled "Oseledec") in 1965 and reported at the International Mathematical Congress in Moscow in 1966.
 A conceptually different proof of the multiplicative ergodic theorem was found by M. S. Raghunathan.
 The theorem has been extended to semisimple Lie groups by V. A. Kaimanovich and further generalized in the works of David Ruelle, Grigory Margulis, Anders Karlsson, and François Ledrappier.
Pavel Sergeyevich Alexandrov (Russian: Па́вел Серге́евич Алекса́ндров ), sometimes romanized Paul Alexandroff or Aleksandrov (7 May 1896 – 16 November 1982), was a Soviet mathematician.
 He wrote about three hundred papers, making important contributions to set theory and topology.
In the mathematical field of topology, the Alexandroff extension is a way to extend a noncompact topological space by adjoining a single point in such a way that the resulting space is compact.
 It is named for the Russian mathematician Pavel Alexandrov.
Pavel Samuilovich Urysohn (Па́вел Самуи́лович Урысо́н ) (February 3, 1898 – August 17, 1924) was a Soviet mathematician of Jewish origin who is best known for his contributions in dimension theory, and for developing Urysohn's Metrization Theorem and Urysohn's Lemma, both of which are fundamental results in topology.
 His name is also commemorated in the terms Urysohn universal space, Fréchet–Urysohn space, Menger–Urysohn dimension and Urysohn integral equation.
 He and Pavel Alexandrov formulated the modern definition of compactness in 1923.
The napkin folding problem is a problem in geometry and the mathematics of paper folding that explores whether folding a square or a rectangular napkin can increase its perimeter.
 The problem is known under several names, including the Margulis napkin problem, suggesting it is due to Grigory Margulis, and the Arnold's rouble problem referring to Vladimir Arnold and the folding of a Russian ruble bank note.
 Some versions of the problem were solved by Robert J. Lang, Svetlana Krat, Alexey S. Tarasov, and Ivan Yaschenko.
 One form of the problem remains open.
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).
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.
In topology, the nerve of an open covering is a construction of an abstract simplicial complex from an open covering of a topological space "X" that captures many of the interesting topological properties in an algorithmic or combinatorial way.
 It was introduced by Pavel Alexandrov.
 and now has many variants and generalisations, among them the Čech nerve of a cover, which in turn is generalised by hypercoverings.
In mathematics, in the theory of discrete groups, superrigidity is a concept designed to show how a linear representation ρ of a discrete group Γ inside an algebraic group "G" can, under some circumstances, be as good as a representation of "G" itself.
 That this phenomenon happens for certain broadly defined classes of lattices inside semisimple groups was the discovery of Grigory Margulis, who proved some fundamental results in this direction.

Question: Who was born first, Pavel Alexandrov or Grigory Margulis?
Answer: Pavel Sergeyevich Alexandrov