source 2007 Hisil--Carter--Dawson compute B = XX1-ZZ1 compute T1 = XX1+ZZ1 compute C = Y1 T1 compute X3 = C-Y1(X1+Z1)^2 compute Z3 = T1 B compute XX3 = X3^2 compute ZZ3 = Z3^2 compute T3 = XX3+ZZ3 compute Y3 = 2 C^2-T3