source 2007 Feng--Wu, first JQN2 doubling formula, plus correction of obvious typos, plus epsilon=1, plus delta=-a, plus common-subexpression elimination parameter a2 assume a2 = 2 a compute XZ1 = X1 Z1 compute U1 = (XZ1+Y1)^2 compute U2 = Y1^2 compute V1 = (X1^2)^2 compute S1 = XZ1^2 compute aS1 = a2 S1 compute T = U2-V1-aS1 compute X3 = U1-U2-S1 compute Y3 = (T+V1)(U2+aS1)+(2 S1)^2 compute Z3 = T-V1