Egidio Astesiano Gianna Reggio Elena Zucca Stores as Homomorphisms and their Transformations. 242-251 1993 conf/mfcs/1993 MFCS db/conf/mfcs/mfcs93.html#AstesianoRZ93 http://dx.doi.org/10.1007/3-540-57182-5_16