@incollection{MauPurVir:82,
  publisher = {Babe\c s-Bolyai University},
  title = {Tolerances on algebras},
  olume = {Preprint no. 2},
  author = {Maurer, I. and Purdea, Ioan and Virag, E.},
  year = 1982,
  pages = {39--75},
  series = {Faculty of Mathematics Research Seminaries},
}