Don't cry to quit, cry to keep going.

The past is a kind of shadow which is always there, whether you choose to ignore it or not.

To be aware of the idea of social structure and to use it with sensibility is to be capable of tracing such linkages among a great variety of milieux.

Theorems are eternal; their proofs are ephemeral.

数学的本质不是使简单的事情复杂化，而是使复杂的事情简单化。