Ralph P. Grimaldi, Discrete and Combinatorial Mathematics,p. 748 6 Temmuz 2015 tarihinde Wayback Machine sitesinde arşivlendi.. Pearson Education (2003)
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Ralph P. Grimaldi, Discrete and Combinatorial Mathematics,p. 748 6 Temmuz 2015 tarihinde Wayback Machine sitesinde arşivlendi.. Pearson Education (2003)