Agostino Cortesi Gilberto Filé William H. Winsborough The Quotient of an Abstract Interpretation. 163-192 1998 202 Theor. Comput. Sci. 1-2 db/journals/tcs/tcs202.html#CortesiFW98 http://dx.doi.org/10.1016/S0304-3975(97)00137-0