At some point, a few years after college, and after learning about Fourier transforms, I eventually endeavored to take a Fourier transform of a Fourier transform. Conceptually, I can imagine not only taking a "2nd level Fourier transform", but "n-level Fourier transforms", where the transform of the transform of the transform, and so on, is taken a number of times. Mathematically and symbolically this could rapidly grow unwieldy, though it would be interesting but difficult