Possible Duplicate:
Countable Sets and the Cartesian Product of them
Sum of two countably infinite sets
I want to solve a problem, this problem is the following:
Prove that if the sets $A$ and $B$ are countable then these sets are also countable:
- $Α \cap B$
- $A \cup B$
- $A \times B$ (Cartesian product of $A$ and $B$)
Thank you very much.