Jan A. Bergstra Manfred Broy J. V. Tucker Martin Wirsing On the Power of Algebraic Specifications. 193-204 1981 conf/mfcs/1981 MFCS db/conf/mfcs/mfcs81.html#BergstraBTW81 http://dx.doi.org/10.1007/3-540-10856-4_85