2 ms·
There's a general result that the set of "All pairs of elements from two countable sets" is, itself, countable. (the Cartesian product of two countable sets is
by roywiggins 12y ago
There's a general result that the set of "All pairs of elements from two countable sets" is, itself, countable. (the Cartesian product of two countable sets is countable).
For example, the set of all pairs of natural numbers can be counted something like this:
1,1
2,1
2,2
1,2
3,1
3,2
3,3
1,3
2,3
...