Differential Equations and the Calculus of Variations
Lev Elsgolts (deceased) was a Doctor of Physico-Mathematical Sciences, Professor at the Patrice Lumumba University of Friendship of Peoples.  His research work was dedicated to the calculus of variations and differential equations.  He worked out the theory of differential equations with deviating arguments and supplied methods for their solution.Lev Elsgolts was the author of many printed works.  Among others, he wrote the well-known books "Qualitative Methods in Mathematical Analysis" and "Introduction to the Theory of Differential Equations with eviating Arguments."In addition to his research work Lev Elsgolts taught at higher schools for over twenty years.