Robert Cori Yves Métivier Approximation of a TRace, Asynchronous Automata and the Ordering of Events in a Distributed System. 147-161 1988 conf/icalp/1988 ICALP db/conf/icalp/icalp88.html#CoriM88 http://dx.doi.org/10.1007/3-540-19488-6_113