1. V. K. Kharchenko and A. Z. Popov, ?Directional derivatives of prime rings,? in: Studies in Ring Theory and Theory of Algebras, Tr. Inst. Mat., Sib. Otd., Akad. Nauk SSSR,16, 183?195 (1989).
2. L. Rowen, ?Generalized polynomial identities,? J. Algebra,34, No. 3, 458?480 (1975).
3. V. K. Kharchenko, ?Derivative identities of prime rings,? Algebra i Logika,18, No. 1, 86?119 (1979).
4. K. I. Beidar and L. V. Mikhalev, ?Orthogonal completeness and algebraic systems,? Usp. Mat. Nauk,40, No. 6, 79?115 (1985).