To astronomers, flat means that the usual rules of geometry are observed - light travels in straight lines, not curves.

对于天文学家来说，平面的宇宙意味着几何学的一般原理将被遵守，光在直线中运行，而不是曲线。

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Only in a flat universe does space obey all the standard geometry-class rules-the angles of a triangle add up to exactly 180 degrees and parallel lines never meet.

只有在平坦的宇宙中，空间才符合标准的几何规律——三角形的内角和精确地等于180度，平行线永远不相交。

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Since rules inferring is faster than geometry computation and requires little time, the rules are of help to improve efficiency of querying spatial data.

由于规则推理比几何计算速度快、内存消耗小，因此推理能够提高基于空间关系的空间数据查询的速度和效率。

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