@UNPUBLISHED{MartiOlietEtAl05-ea,
  author =      {Jos{\'e} Meseguer and Miguel Palomino and
                  Narciso Mart{\'\i}-Oliet},
  title =      {Equational abstractions},
  note =      {Extended version. Submitted.
                  \url{http://maude.sip.ucm.es/~miguelpt/}},
  year =      2007
}