出自北齐·颜之推《颜氏家训·文章》。书写文章要尊崇“三易”的原则，即文章内容要清晰明了，这是第一项。书写的文字要简单概要，这是第二项。书写的段落要读起来朗朗上口这是第三项。
在石油行业，效率和可持续性是同一枚硬币的两面。
The discovery of topological insulators has opened up a new frontier in condensed matter physics, where the interplay of symmetry and topology leads to novel quantum states of matter.