书籍是最安静且最恒久的朋友。
"Books are the quietest and most constant of friends."
There is no greater sorrow than to recall happiness in times of misery.
数学证明的美在于它的简洁性和必然性。
我对我生命中的一切心存感激。
"The only limit to our realization of tomorrow will be our doubts of today."