I like the one that snake around, $0, -1, 1, -2, 2, -3, 3,\ldots$

So it goes


  $$\begin{cases}f: \Bbb N\to \Bbb Z \\ f(2n)=n-1 \\ f(2n-1)=-n\end{cases}$$


If you want it to go the other way, you just reverse the idea and compute the inverse of $f$.

How to show the integers have same cardinality as the natural numbers?
I am trying to perform loadkeys operation. For normal user, I am getting permission denied 
error.

the error is as follows.

&lt;tim@testps&gt;~% loadkeys mykeys
Loading /usr/tim/mykeys
Keymap 0: Permission denied
Keymap 1: Permission denied
Keymap 2: Permission denied
KDSKBENT: Operation not permitted
loadkeys: could not deallocate keymap 3

