To every action there is always opposed an equal reaction； or， the mutual actions of two bodies upon each other are always equal， and directed to contrary parts.

唯一的好是知识，唯一的恶是无知。

直到故事发生了最坏的转折，它才算结束。

关系模型基于谓词逻辑和集合论，为数据库管理提供了坚实的数学基础。