We will be concerned primarily with bijective proofs, i.e., showing that two sets have the same number of elements by exhibiting a bijection (one-to-one correspondence) between them.
我们主
的是
射的证明，也就是透过
两个集合间建立
个射（
映成的函数）来证明它们的元素个数相等。
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学之美 What we now call functions mathematical functions, which are Continuous that is that are not formed out of a discrete sets like the counting numbers for instance Newton there were already
们现在称之为函
学函，它们是连续， 也就是说，它们不是由像计字那样离散
构成。 举例来说，在牛顿时代， 已经存在一些方法来解决涉及诸如求曲线下面积和曲线切线等问题， 但这些方法仅适用于某些特定且有限曲线类型。
选取四个元素
