数据库可以为每个节点分配顺序号，这样就知道每个节点的位置，可以在常数时间内比较两个节点的文档顺序。
The database can assign sequence Numbers to each node so that it knows the position of each node and can compare the document order of two nodes in constant time.
相反，在宇宙中，该常数会随所在的位置发生变化。
Rather, it seems to vary from place to place within the universe.
爱因斯坦认为存在一个宇宙常数来填补现在暗能量的位置。
Einstein proposed the existence of something he called the cosmological constant, to fulfil the role now assigned to dark energy.
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