The Liskov Substitution Principle is a fundamental concept in object-oriented programming, ensuring that derived classes can be used in place of their base classes without altering the correctness of the program.

机械师应当坐在杠杆、螺丝、楔子、轮子等中间，就像诗人坐在字母中间一样，将它们视为他思想的展示。

建筑是使不可见之物可见的艺术。