作者thank1984 (thankakimo)
看板Grad-ProbAsk
标题[理工] 离散-Countable
时间Thu Mar 19 16:09:53 2009
题目: If A and B are two countable sets,show that A*B is also countable.
问题: 请问各位大大这题要如何解答呢 ?? 烦请指导 感谢
--
※ 发信站: 批踢踢实业坊(ptt.cc)
◆ From: 163.14.68.41
1F：推 PALAPO:我只想到 N*N -> N 这样证 不知道对不对 03/19 16:11
2F：→ SansWord:A -> N, B -> N 03/19 17:39
3F：→ SansWord:A*B -> N -> N -> N 03/19 17:40
4F：→ SansWord:so, A*B is countable 03/19 17:40
5F：→ SansWord:第二行打错...更正:A*B -> N*N -> N 03/19 17:40
6F：→ thank1984:了解了 感谢S大和P大解答 03/19 21:10