1. Zhang W (2004) 2nd ed. Wiley-Liss, New York, p 106
2. Simon R (2003) 2nd ed. New York, p 37–40
3. Blalock EMA (2003) Kluwer Academic, New York, p 15
4. Baldi P (2002) 2nd ed. Cambridge University Press, p 117
5. Hardiman G (2003) The Nuts and Bolts Series. Independent Publishers Group