If the glass were kept hot enough, it would flow over the molten tin until the topsurface was also flat, horizontal and perfectly parallel to the bottom surface.
如果玻璃保持足够的温度，它就会在熔化的锡中流动，直到顶部表面也变得平整、水平，与底部表面完全平行。
2
Its carved underside shapes the lobby below, while its topsurface is the floor plate of the exhibition space.
凹陷的下方雕刻形成了大堂的下方，而凹陷的上表面则是展览空间的底板。
3
So, that means you have to figure out what's the bottom surface of your solid, and what's the topsurface of your solid?