A leader has the vision and conviction that a dream can be achieved. He inspires the power and energy to get it done.

The PAC learning framework provides a formal way to quantify the learnability of a concept class.

翻译：真正的朋友，顺境时不添虚假繁华，逆境时不改变初心，富贵时不忘记旧交，这样的情谊才珍贵。