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- Herstein , I. N. ( 1972 ). Noncommutative Rings . Moscow : Mir .
- Lang , S. ( 1968 ). Algebra . Moscow : Mir .
- Obreshkov , N. ( 1962 ). High Algebra . Sofia : Nauka i Iskustvo .
- Van der Waerden , B. L. ( 1976 ). Algebra . Moscow : Nauka .
- #Communicated by A. Facchini.