source 2007 Bernstein--Lange
parameter cc2
assume cc2 = 2*c*c
assume Z1 = 1
compute B = (X1+Y1)^2
compute C = X1^2
compute D = Y1^2
compute E = C+D
compute J = E-cc2
compute X3 = c(B-E)J
compute Y3 = c E(C-D)
compute Z3 = E J
