免费的疫苗比昂贵的治疗更有价值，但更难推广。
Free vaccines are more valuable than expensive treatments, yet harder to promote.
有能力给予当然比有能力接受来得更让人愉快。
To understand the mind, study its operations in real life.
数学不是关于数字、方程、计算或算法的：它是关于理解的。
The materials I use are witnesses of time.