Basic embeddings and Hilbert's 13th problem on superpositions (in Russian)

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This note is purely expository. We show how in the course of the Kolmogorov-Arnold solution of Hilbert's 13-th problem on superpositions there appeared the notion of a basic embedding. A subset K of R² is basic if for each continuous function f:K->R there exist continuous functions g,h:R->R such that f(x,y) = g(x) + h(y) for each point (x,y) in K. We present descriptions of basic subsets of the plane and graphs basically embeddable into the plane (solutions of Arnold's and Sternfeld's problems). We present some results and open problems on the smooth version of the property of being basic. This note is accessible to undergraduates and could be an interesting easy reading for mature mathematicians.