问题6： (1) trianglecount =0 你能解释这个原理的应用吗？ (2) for i=1 to n 参考书上证明增长3元组集合和3元素子集等势时，这段 话的用意是什么？ Because the three elements of an increasing triple are different,the subset is a three-element set;so, we have a function from increasing triples to three- element sets. Principle 1.5 (Bijection Principle) Two sets have the same size if and only if there is a one-to-one function from one set onto the other.参考书上证明增长3元组集合和3元素子集等势时，这段 话的用意是什么？ Because the three elements of an increasing triple are different, the subset is a three-element set; so, we have a function from increasing triples to three￾element sets