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The Earth-Moon problem is a special case of the empire problem for countries with disjoint regions, with one region of each country lying on the Earth and one on the Moon (Ringel 1959; Frederickson 2002, p. 32). The additional constraint means that fewer than 12 colors might suffice. And in fact, Ringel (1959) gave an example requiring only 8 colors. Gardner (1980) reported an example requiring 9 colors, but it is not known if configurations exist requiring 10, 11, or 12 colors (Frederickson 2002, p. 32).
Frederickson, G. N. Hinged Dissections: Swinging & Twisting. New York: Cambridge University Press, 2002.
Gardner, M. "Mathematical Recreations: The Coloring of Unusual Maps Leads Into Uncharted Territory." Sci. Amer. 242, 14-22, Feb. 1980.
Ringel, G. Färbungsprobleme auf Flachen und Graphen. Berlin: Deutsche Verlag der Wissenschaften, 1959.
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تجربة بسيطة مدتها 3 دقائق تحسن النظر كثيرا
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الصين.. تطوير محفز نانوي رخيص الثمن لتنقية المياه من النترات
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بحضور علمائي ورسمي .. العتبة العلوية المقدسة ترفع راية الحزن والحداد إيذاناً بحلول شهر محرم الحرام
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