The first introduction to algebraic specification of abstract data types. Contains lots of examples, too. Doesn't have an actual Bibtex citation, but this is a text version: J. V. Guttag, J. J. Horning, The algebraic specification of abstract data types, Acta Informatica, Volume 10, Issue 1, Mar 1978, Pages 27 - 52, DOI 10.1007/BF00260922, URL http://dx.doi.org/10.1007/BF00260922