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2. Cramér, H., "Random Variables and Probability Distributions", Cambridge Tract. Math., 36 (1937).
3. Bagnold, R. A., "The Physics of Blown Sand and Desert Dunes" (London: Methuen, 1941).
4. Kapteyn, J. C., "Skew Frequency Curves in Biology and Statistics" (Groningen: Noordhoff, 1903).
5. Kapteyn, J. C., Rec Trav. Bot. Neerland, 13, 105 (1916).