source 2009.04.27 Bernstein--Lange
assume Z1 = 1
assume Z2 = 1
compute H = X2-X1
compute HH = H^2
compute HHHH = HH^2
compute Z3 = 2 H
compute ZZ3 = 4 HH
compute J = 2 ((H+HH)^2-HH-HHHH)
compute r = 2(Y2-Y1)
compute V = X1 ZZ3
compute X3 = r^2-J-2 V
compute Y3 = r(V-X3)-2 Y1 J
compute T3 = 16 a HHHH