O.K. I know everyone wants to hear more about this so here it is: 1+1=2 works in Z
1+1=0 works in Z2
The difference is in the addition opperators (+) which are not the same, thus the problems differ.
However, this is all irrelevant for us, unlike the link im about to post in the Fastest guitarist... thread. I know he's probbably not the fastest, but do check it out.