International politics is a ruthless and dangerous business, and it is foolish to expect states to behave according to moral principles.

Every mathematical problem is a puzzle waiting to be solved, and every solution is a step towards greater understanding.

The purpose of abstraction is not to be vague, but to create a new semantic level in which one can be absolutely precise.

如果你想飞翔，就必须放弃拖累你的东西。