t0 = X1+Y1 B = t0^2 C = X1^2 D = Y1^2 E = a*C F = E+D t1 = B-C t2 = t1-D t3 = F-2 X3 = t2*t3 t4 = E-D Y3 = F*t4 t5 = F^2 t6 = 2*F Z3 = t5-t6