source 2008 Sutherland
assume ZZ2 = 1
assume ZZZ2 = 1
compute U2 = X2 ZZ1
compute S2 = Y2 ZZZ1
compute P = U2-X1
compute R = S2-Y1
compute PP = P^2
compute PPP = P PP
compute Q = X1 PP
compute X3 = R^2-PPP-2 Q
compute Y3 = R (Q-X3)-Y1 PPP
compute ZZ3 = ZZ1 PP
compute ZZZ3 = ZZZ1 PPP