People can be divided into these types: strangers, acquaintances, familiar people, friends, and close friends. True friendship isn't about compliments to your face, but whether you're mentioned when they talk about friends behind your back.

Mathematics is not about numbers, equations, computations, or algorithms: it is about understanding.

文章以气势为主，气势的清新或浑浊有其内在规律，不能勉强达到。