@incollection{PurBot:92b,
  title = {Equivalent extensions},
  year = 1992,
  booktitle = {Proc. of the Conference on Algebra},
  pages = {1--6},
  publisher = {Babe\c s-Bolyai University},
  olume = {Preprint no. 1},
  author = {Purdea, Ioan and Both, Nicolae},
  series = {Faculty of Mathematics Research Seminaries},
}