One's deceased father grind mathematics god asks for advice, and plans to take a master's degree. Is it necessary to ask the proof of the definition in the number two exam, the definition in the textbook, and the proof of nature? Some definitions need to be looked at, such as the definition of continuity, derivative, differentiability, partial derivative and so on. Others have lower requirements, such as the definition of limit and definite integral. Some don't need to see, such as the definition of multiple integral, the definition of surface integral and so on. Different definitions need to be treated differently and cannot be generalized. Don't look at the proof of nature and theorem, just remember the conclusion and use it when doing the problem.