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arxiv: 1412.7996 · v1 · pith:X7EU2MXJnew · submitted 2014-12-26 · 🧮 math.CO

Splitting necklaces and measurable colorings of the real line

classification 🧮 math.CO
keywords everylinerealcoloringmeasurablecolorcoloredcolors
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A (continuous) necklace is simply an interval of the real line colored measurably with some number of colors. A well-known application of the Borsuk-Ulam theorem asserts that every $k$-colored necklace can be fairly split by at most $k$ cuts (from the resulting pieces one can form two collections, each capturing the same measure of every color). Here we prove that for every $k\geq 1$ there is a measurable $(k+3)$-coloring of the real line such that no interval can be fairly split using at most $k$ cuts. In particular, there is a measurable $4$-coloring of the real line in which no two adjacent intervals have the same measure of every color. An analogous problem for the integers was posed by Erd\H{o}s in 1961 and solved in the affirmative in 1991 by Ker\"anen. Curiously, in the discrete case the desired coloring also uses four colors.

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