source 2007 Feng--Wu, second JQN2 doubling formula, plus epsilon=1, plus delta=-a, plus common-subexpression elimination
appliesto 2xyz
parameter a2
assume a2 = 2 a
parameter c2
assume c2 = 2 c
compute XX1 = X1^2
compute XZ1 = X1 Z1
compute T1 = XZ1^2
compute T2 = Y1^2
compute S1 = (T2+c2 T1)^2
compute X3 = (XZ1+Y1)^2-T1-T2
compute V = X3^2
compute Y3 = S1-c V
compute Z3 = T2-a2 T1-2 XX1^2