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· Let A and B be sets. If A and B are countable, then A ∪...

· Let A and B be sets. If A and B are countable, then A ∪ B is countable.

· Let A and B be sets. If A and B are infinite, then A ∪ B is infinite.

· Let A and B be sets. If A and B are countably infinite, then A ∪ B is countably infinite.

Find nontrivial sets A and B such that A ∪ B = Z, then use these theorems to show Z is countably infinite.

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