If you borrow something， try to return it in better shape than you received it. Clean it， sharpen it， fill it up.
如果你借了什么东西，试着在归还的时候把它变得比你借到时的状态更好。清洁它、打磨它、填充它。
A mathematician's work is mostly a solitary pursuit, but it builds on the work of many others.
不过话得说回来，没有一桩事是容易的。