I want to show that no 1-private deterministic protocol exists for calculating a sum of $n \geq 3$ parties (within the realms of Perfect rather than Computational Security). I'm having trouble showing that as I have to show that for any protocol, meaning I've no idea what messages are being sent.
I thought about showing privacy violation by showing that knowing the sum, a party may gain information about others, but obviously a Simulator could do that as well.