source 2009.04.27 Bernstein--Lange
assume Z1 = 1
compute XX = X1^2
compute A = 2 Y1^2
compute AA = A^2
compute U = 2 AA
compute S = (X1+A)^2-XX-AA
compute M = 3 XX + T1
compute X3 = M^2 - 2 S
compute Y3 = M(S-X3)-U
compute Z3 = 2 Y1
compute T3 = 2 U T1