On Wiener norm of subsets of Z_p of medium size
  We give a lower bound for Wiener norm of characteristic function of subsets A from Z_p, p is a prime number, in the situation when exp((log p/log log p)^{1/3}) \le |A| \le p/3. 
Sergei V. Konyagin, Ilya D. Shkredov
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