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2. [79] This article uses material from the Wikipedia article Petroleum industry, which is released under the Creative Commons Attribution-Share-Alike License 3.0.
3. [78] This article usesmaterial from the Wikipedia article Gold reserve, which is released under the Creative Commons Attribution-Share-Alike License 3.0.
4. Recherches mathématiques sur la loi d’accroissement de la population;Verhurst;Nouveaux Mémoires de l’Académie Royale des Sciences et Belles Lettres de Bruxelles,1845