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TOT 262 1990 Spring A S6 ink-blots on a white paper square

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June 8, 2024
combinatoricscombinatorial geometrygeometry

Problem Statement

There are some ink-blots on a white paper square with side length aa. The area of each blot is not greater than 11 and every line parallel to any one of the sides of the square intersects no more than one blot. Prove that the total area of the blots is not greater than aa.
(A. Razborov, Moscow)