Proof. Suppose the induction principle were false.Then there would exist an assertion P that would satisfy conditions (i)and (ii)of thethe- orem,but P(n)would be false for some n e Z+.So let A =k e Z:P(k)is false}.Our supposition implies that A is nonempty.By the well-ordering principle [p.135],the set A has a minimum.Let m denote this minimum.By condition (i),m 1.Since m eZ+,it follows that m >2.Consider the integer n m-1 1.Since n<m and m is the minimum of A,we know that ngA.Thus P(n)is true. By condition (ii),P(n+1)is true too.But P(n+1)=P(m),so P(m) must also be true,a contradiction. 几个问题：1，良序性如果没有，数学归纳法会出什么问题？ 2,两个前提条件分别在哪里被使用？几个问题：1，良序性如果没有，数学归纳法会出什么问题？ 2，两个前提条件分别在哪里被使用？