1. Tukey, J.W.: ‘Nonlinear (nonsuperposable) methods for smoothing data’, EASCON record, 1974), p. 673
2. Pratt, W.K.: Digital image processing, (University of Southern California, Image Processing Institute 1975 January)
3. Knuth, D.E.: Sorting and searching, (Addison-Wesley, Reading, Mass. 1973)