“物质”不是唯一的事实标准：还存在心理事实，而且无法以任何的物质方式来解释、证明、或辩驳它。

The development of formal systems has revolutionized our understanding of mathematics.

Efficiency is doing things right; effectiveness is doing the right things.

在距离与重量成反比的情况下，物体处于平衡状态。