The characteristic function of a set is one in the set and zero outside [1]. Take fourier transform of this function. Fourier transform is a linear operator. Tu

The characteristic function of a set is one in the set and zero outside [1]. Take fourier transform of this function. Fourier transform is a linear operator. Turn handle, bingo. [1] http://en.wikipedia.org/wiki/Indicator_function http://en.wikipedia.org/wiki/Indicator_function