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Point Guard……这一连串的留言出现在天启的主页。Rules for INPUT can exist in: mangle table, filter table, and nat table in centos7, not in centos6).A: You are mature and steady, stick to yourself, and often find that you are out of step with this fast-changing era.　野心勃勃的金融才子不顾一切地想要成为创业明星，于是通过谎言、作弊和骗局，让自己虚有其表的公司走向成功。The Liskov Substitution Principle (LSP) is one of the basic principles of object-oriented design. The Richter substitution principle says that wherever a base class can appear, subclasses can certainly appear. LSP is the cornerstone of inheritance reuse. Only when derivative classes can replace base classes and the functions of software units are not affected can base classes be truly reused, and derivative classes can also add new behaviors to base classes. The Richter substitution principle is a supplement to the "open-close" principle. The key step to realize the "open-close" principle is abstraction. The inheritance relationship between the base class and the subclass is the concrete realization of abstraction, so the Richter substitution principle is the specification of the concrete steps to realize abstraction. --From Baidu