@Thomas Richard Thank you, I know that diffalg is deprecated and replaced by DifferentialAlgebra. However, I don't use the standard diffalg from Maple, but its later version diffalg(04) (http://www-sop.inria.fr/members/Evelyne.Hubert/diffalg/), which was not a part of Maple. Actually, I have Maple 2015, but procedure Rosenfeld_Groebner of diffalg(04) does not run with my input under Maple 2015, so I have to use Maple 9. I use diffalg(04) because its version of Rosenfeld_Groebner allows using non-commutative derivations, which is important to me as I am trying to simplify the task using the high symmetry of my problem (it is invariant under the Poincare group) and methods of Hubert, E. Differential Algebra for Derivations with Nontrivial Commutation Rules, Journal of Pure and Applied Algebra (2005), Volume 200, Issues 1-2. (http://www.ens-lyon.fr/LIP/Arenaire/SYMB/teams/cafe/cafe3.pdf) . As far as I know, there is no such functionality in DifferentialAlgebra.