Random matching is often used in economic models as a means of introducing uncertainty in sequential decision problems. We show that random matching processes that satisfy standard proportionality laws are not unique. We give conditions on the payo¤s and transitions functions of sequential decision models that insure that the models are robust to the non-uniqueness of the matching process. Unde...

The trace equivalence of BPP was shown to be undecidable by Hirshfeld. We show that the trace equivalence remains undecidable even if the number of labels is restricted to two. The undecidability result holds also for the simulation of two-label BPP processes. These results imply undecidability of some behavioral type systems for the π-calculus.