Martin Große-Rhode Francesco Parisi-Presicce Marta Simeoni Formal Software Specification with Refinements and Modules of Typed Graph Transformation Systems. 171-218 2002 64 J. Comput. Syst. Sci. 2 http://dx.doi.org/10.1006/jcss.2001.1800 db/journals/jcss/jcss64.html#Grosse-RhodePS02