> If you can map all elements from the first infinite to the second, but not the other way around, the second is larger than the first. This seems simple enoug

> If you can map all elements from the first infinite to the second, but not the other way around, the second is larger than the first. This seems simple enough but it's still very much counter intuitive when comparing say all the natural numbers with only the even numbers. An intuitive mapping would lead you to think there are more naturals than evens, but math says these two infinites are of the same size.