The Liskov Substitution Principle is a fundamental concept in object-oriented programming, stating that objects of a superclass should be replaceable with objects of a subclass without affecting the correctness of the program.

能用钱解决的问题，都不是真的问题。

The most important thing in trading is to protect your capital.

The sustainable development of the coal industry requires the coordinated efforts of policy, technology, and the market.