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