How to count like a mathematician
Counting seems like a trivial thing that we all do with ease. But pulling out the essence, the underlying pattern of counting, allows for a whole new world to open before our eyes.
We can count objects with other objects, we can count infinities, and we can count very strange sets! All stemming from this idea of a bijective function.
If you would like to know the answer to problem 2 of "try yourself":
There are 6 such bijections! Can you find them all?