O’Connor, J. J. – Robertson, E. F.: August Ferdinand Möbius School of Mathematical and Computational Sciences, University of St Andrews. Arkistoitu 26.9.2007. Viitattu 22.5.2007. (englanniksi)
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O’Connor, J. J. – Robertson, E. F.: August Ferdinand Möbius School of Mathematical and Computational Sciences, University of St Andrews. Arkistoitu 26.9.2007. Viitattu 22.5.2007. (englanniksi)