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为了研究问题的方便和统一,在本文中所建立的正方体模型统一记为:正方体A1B1C1D1-A2B2C2D2,(画图时字母位置:A1B1C1D1在下,A2B2C2D2在上)简记为:正方体A1C2,且棱长为1.
In order to study the convenience and unity of the problem, the cube model established in this paper is unified as: cube A1B1C1D1-A2B2C2D2, (A1B1C1D1 is lower and A2B2C2D2 is upper) is abbreviated as: cube A1C2 and the edge length is 1 .