source 2007 Feng--Wu, first JQN2 doubling formula, plus correction of obvious typos, plus epsilon=1, plus substitution delta=-a
parameter a2
assume a2 = 2 a
compute U1 = (X1 Z1+Y1)^2
compute U2 = Y1^2
compute V1 = (X1^2)^2
compute S1 = (X1 Z1)^2
compute T = U2-V1-a2 S1
compute X3 = U1-U2-S1
compute Y3 = (T+V1)(U2+a2 S1)+4 S1^2
compute Z3 = T-V1