Hi, this forum looks great and I'm glad to have found it. Now to my first question. Basically, I want to know if there is any literature on using the Fourier transform on unordered sets in order to see if two sets intersect (and how many times). I welcome any alternative approaches, esp. if this idea makes no sense. From http://homepages.inf.ed.ac.uk/rbf/HIPR2/fourier.htm I see, "The Fourier Transform is used if we want to access the geometric characteristics of a spatial domain image. Because the image in the Fourier domain is decomposed into its sinusoidal components, it is easy to examine or process certain frequencies of the image, thus influencing the geometric structure in the spatial domain." So say I have an image, and I copy a piece out of that image. Then I use the Fourier transform to make my pretty complex valued image. I do the same to the piece I copied. Is there any way I can determine that the piece also exists within the first complex valued image? If so how? Is there a better way to determine if two sets (or images) intersect, than by using the Fourier transform?