source 2007 Bernstein--Lange compute XX = X1^2 compute YY = Y1^2 compute YYYY = YY^2 compute ZZ = Z1^2 compute S = 2 ((X1+YY)^2-XX-YYYY) compute M = 3 XX+a ZZ^2 compute T = M^2-2 S compute X3 = T compute Y3 = M (S-T)-8 YYYY compute Z3 = (Y1+Z1)^2-YY-ZZ