Rance Cleaveland Matthew Hennessy Testing Equivalence as a Bisimulation Equivalence. 11-23 1989 conf/avmfss/1989 Automatic Verification Methods for Finite State Systems db/conf/avmfss/avmfss1989.html#CleavelandH89 http://dx.doi.org/10.1007/3-540-52148-8_2