source 2008.02.25 Hisil--Wong--Carter--Dawson, page 10, bottom compute X3 = (XY1-YZ1)(XZ1+2(XX1+ZZ1)) compute Y3 = (XZ1-XY1)(YZ1+2(YY1+ZZ1)) compute Z3 = (YZ1-XZ1)(XY1+2(XX1+YY1)) compute XX3 = X3^2 compute YY3 = Y3^2 compute ZZ3 = Z3^2 compute XY3 = (X3+Y3)^2-XX3-YY3 compute XZ3 = (X3+Z3)^2-XX3-ZZ3 compute YZ3 = (Y3+Z3)^2-YY3-ZZ3