source 2006 Doche--Icart--Kohel "Efficient scalar multiplication by isogeny decompositions", page 198, middle display
parameter b
assume b = 4 a - 9
parameter c
assume c = -3 a
compute A = (X1+3 ZZ1)^2
compute B = a ZZ1 A
compute Xt = Y1^2+B
compute Yt = Y1(Y1^2-3 B)
compute Zt = X1 Z1
compute C = Zt^2
compute D = (b C-Xt)^2
compute E = c C D
compute X3 = (Yt^2+E)
compute Y3 = Yt(X3-4 E)
compute Z3 = 3 Xt Zt
compute ZZ3 = Z3^2