So how did Cantor get the idea that the set is countable? And what exactly does "countable" mean?
Test your knowledge before we investigate what countable means, by choosing the one correct answer:
1. is countable because it contains natural numbers.
2. is countable because you can count the elements.
3. is countable because each element has a unique name.
4. is countable because every element has an ordinal value.
So, what do you think is the ONLY correct answer?
I will reveal the answer only if at least one person attempts the question.
You will be surprised at what it means to be countable. I can bet a few dollars that many topologists never fully understood this concept.