Some systems were hierarchical; others used flat or semi-flatspaces.
一些系统采用层次结构，另一些则使用扁平或半扁平空间。
2
From this point of view these flatSpaces around us turn out to be one possible source of dark energy for the accelerating expansion of the Universe.
从这个角度看，我们周围的这些平面空间可能是暗能量的一个来源，而正是它让宇宙加速膨胀。
3
On a topographic map of the United States, the mountains look like jagged masses, the plains like vast open flatspaces, and the rivers like meandering threads.