For every dollar you spend purchasing something substantial, expect to pay a dollar in repairs, maintenance, or disposal by the end of its life.
数学家是能在定理间找到类比的人;更好的数学家能在理论间看到类比;而最优秀的数学家能注意到类比之间的类比。
The test of a first-rate intelligence is the ability to hold two opposed ideas in mind at the same time and still retain the ability to function.