= Lacunary Fourier series
{title2=$n_{j+1}/n_j\geq q>1$}
A Hadamard-lacunary <Fourier series> has nonzero frequencies supported on a positive sequence with the displayed gap ratio, possibly together with its negatives and finitely many extra modes. Such gaps strongly restrict additive frequency relations. They make moment estimates resemble those of independent random variables. For a ratio greater than three, the <strongly lacunary polynomial L1-L2 bound> follows directly by enumerating fourth-moment pairings.
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