source 2008 Bernstein--Lange--Rezaeian Farashahi appliesto xy-1 compute A = X1^2 compute B = A^2 compute C = Y1^2 compute D = C^2 compute E = A + C compute F = 1/(d1 + E + B + D) compute X3 = (d1 E + A + B) F compute Y3 = X3 + 1 + d1 F