@article{A_1,
  AUTHOR =  {Blake, I. K:},
  TITLE =  {Codes over certain rings.},
  JOURNAL =  { Inform. Contr.},
  YEAR =  {1972},
  NUMBER =  {20},
  PAGES =  {396-404},
}

@article{A_2,
 author = {Bourbaki,  N.:},
 title = {Algebra, Chapters 1-3.},
 journal = {Springer-Verlag},
 year = {1989},
 address = { New-York}
 }