Hi,
Okay thanks, think I see what you're saying. Is it enough to say..
since (a+b)(a-b)\equiv 0 \pmod p then
a+b=np or a-b=kp where a, b \in \left \{ 1, ..., p-1 \right \}
if a-b=kp then a-b will always be < p and hence k is 0. While 0 < a+b < 2p . Hence n is 1 as we've already said...