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arXiv · 1002.2554

Sum-product estimates for rational functions

Boris Bukh·Jacob Tsimerman
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Abstract

We establish several sum-product estimates over finite fields that involve polynomials and rational functions. First, |f(A)+f(A)|+|AA| is substantially larger than |A| for an arbitrary polynomial f over F_p. Second, a characterization is given for the rational functions f and g for which |f(A)+f(A)|+|g(A,A)| can be as small as |A|, for large |A|. Third, we show that under mild conditions on f, |f(A,A)| is substantially larger than |A|, provided |A| is large. We also present a conjecture on what the general sum-product result should be.

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Boris Bukh, Jacob Tsimerman. 2011-04-25. Sum-product estimates for rational functions. https://doi.org/10.1112/plms%2Fpdr018

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