Ittai Balaban Amir Pnueli Lenore D. Zuck Modular Ranking Abstraction. 5-44 2007 18 Int. J. Found. Comput. Sci. 1 http://dx.doi.org/10.1142/S0129054107004553 db/journals/ijfcs/ijfcs18.html#BalabanPZ07