source 2009.04.01 Bernstein--Lange compute ZZ1 = Z1^2 compute ZZ2 = Z2^2 compute U1 = X1 ZZ2 compute U2 = X2 ZZ1 compute S1 = Y1 Z2 ZZ2 compute S2 = Y2 Z1 ZZ1 compute H = U2-U1 compute I = (2 H)^2 compute J = H I compute r = 2(S2-S1) compute V = U1 I compute X3 = r^2-J-2 V compute Y3 = r(V-X3)-2 S1 J compute Z3 = ((Z1+Z2)^2-ZZ1-ZZ2) H compute ZZ3 = Z3^2 compute T3 = a ZZ3^2