[理工] 離散-Countable

[thank1984 (thankakimo)]

題目: If A and B are two countable sets,show that A*B is also countable.

問題: 請問各位大大這題要如何解答呢 ?? 煩請指導 感謝

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推 PALAPO:我只想到 N*N -> N 這樣証 不知道對不對
→ SansWord:A -> N, B -> N
→ SansWord:A*B -> N -> N -> N
→ SansWord:so, A*B is countable
→ SansWord:第二行打錯...更正:A*B -> N*N -> N
→ thank1984:瞭解了 感謝S大和P大解答