※ 引述《hiei81 (宝贝。永远)》之铭言：
: ※ 引述《pikahacker (Beat Cal)》之铭言：
: : 1. Prove that every tournament contains a Hamiltonian path.
: : (Tournament map: a directed graph such that for every pair of distinct
: : vertices
: : u and v, there is either an edge from u to v or v to u, but never both.)
: : (I can prove this easily by double induction, but I heard there is a
: : classic proof by strong induction. How?)
: 回darkseer，没有interestingly，请爱用it is interesting that...:)
呃...我错了，有interestingly这种用法:p
通常是讲：..., more interestingly, ....
然后double induction应该是指设f(k)和f(k+1)成立，则f(k+2)成立，
且初始条件f(1),f(2)成立
strong induction是指f(1)成立且f(1),f(2),...,f(k)均成立时，则f(k+1)成立
(数学归纳法第二形式)
而我们使用的证明方法既不是double induction也不是strong induction,
只是单纯的数学归纳法第一形式
关于数学归纳法可参阅：
http://www.soe.ucsc.edu/classes/cmpe177/Fall02/induction.pdf