source 2008 Sutherland
compute U1 = X1 ZZ2
compute U2 = X2 ZZ1
compute S1 = Y1 ZZZ2
compute S2 = Y2 ZZZ1
compute P = U2-U1
compute R = S2-S1
compute PP = P^2
compute PPP = P PP
compute Q = U1 PP
compute X3 = R^2-PPP-2 Q
compute Y3 = R (Q-X3)-S1 PPP
compute ZZ3 = ZZ1 ZZ2 PP
compute ZZZ3 = ZZZ1 ZZZ2 PPP