source 2009.04.27 Bernstein--Lange
assume Z2 = 1
compute ZZ1 = Z1^2
compute H = X2 ZZ1-X1
compute HH = H^2
compute I = 4 HH
compute J = H I
compute r = 2(Y2 Z1 ZZ1-Y1)
compute V = X1 I
compute X3 = r^2-J-2 V
compute Y3 = r(V-X3)-2 Y1 J
compute Z3 = (Z1+H)^2 - ZZ1 - HH
compute ZZ3 = Z3^2
compute T3 = a ZZ3^2