Could this be somewhat of a start:
I have been given a task to find a function which satisfies:
1. Definition area for is
2. Value area for is the amount/quantity by the equivalentclass of ~
3. f is injective
4. f is surjectiv
5. for all og in
What is done is actually to complete the quantity theoretical constuction of all integers from the natural numbers.
I actually have no idea where to start! Feel free to point me in a direction, all help is gratefully accepted!