拓扑学是对图形在任何变形下保持不变的性质的研究。
"A book is a dream that you hold in your hand."
Civilization will not last, freedom will not survive, peace will not be kept, unless a very large majority of the people unite to defend them.
量子力学的数学形式不仅是一种工具,更是一种揭示自然深层结构的语言。