source 2015 Chuengsatiansup compute YY = Y1^2 compute aXX = a X1^2 compute Ap = YY + aXX compute B = 2(2 Z1^2 - Ap) compute xB = aXX B compute yB = YY B compute AA = Ap (YY - aXX) compute F = AA - yB compute G = AA + xB compute xE = X1 (yB + AA) compute yH = Y1 (xB - AA) compute zF = Z1 F compute zG = Z1 G compute X3 = xE zF compute Y3 = yH zG compute Z3 = zF zG compute T3 = xE yH