水为万古无情绿，酒是千龄不老丹。
出自《花前劝酒吟》。水是万古以来的最无情的绿色，酒是千年以来可以让人长寿不老的丹药。
It takes considerable knowledge just to realize the extent of your own ignorance.
The only limit to our realization of tomorrow is our doubts of today.
数学的本质在于它的自由。