Onto function with domain of natural numbers and co-domain of integers I'm trying to find an onto function f: $\mathbb{N}$ → $\mathbb{Z}$
This is a new concept I'm learning, and I'm not sure how this would be written. Just need one clear example so I can practice with other examples. Thanks.

I'm going to assume we can construct $\Bbb N x \Bbb N$
We want to define f: $\Bbb N x \Bbb N \to \Bbb Z $ by $f (n_1,n_2) = n_1 - n_2$
Then we can show for any $z \in \Bbb Z $ there exists $(n_1,n_2) $ s.t. $f (n_1,n_2) = z $
