Bernd Krieg-Brückner Algebraic Specification and Fundamentals for Transformational Program and Meta Program Development. 36-59 1989 conf/tapsoft/1989-2 TAPSOFT, Vol.2 db/conf/tapsoft/tapsoft89-2.html#Krieg-Bruckner89 https://doi.org/10.1007/3-540-50940-2_26