David J. Pym Peter W. O'Hearn Hongseok Yang Possible worlds and resources: the semantics of BI. 257-305 2004 315 Theor. Comput. Sci. 1 http://dx.doi.org/10.1016/j.tcs.2003.11.020 db/journals/tcs/tcs315.html#PymOY04