1. Gröbnerbasen in nichtkommutativen Algebren und ihre Anwendung;Apel;Dissertation,1988
2. G-algebras;Apel;Contemp. Math.,1992
3. An algorithm for calculations in enveloping fields of Lie Algebras;Apel;Proc. Conf. Comp. Alg.,1985
4. An algorithm for calculations in envelopping fields of Lie algebras;Apel;J. Symbolic Comput.,1988