We have implemented a parallel graph reducer on a commerciallyavailable shared memory multiprocessor (a SequentSymmetryTM), that achieves real speedup comparedto a a fast compiled implementation of the conventional Gmachine.Using 15 processors, this speedup ranges between5 and 11, depending on the program.Underlying the implementation is an abstract machinecalled the h; Gi-machine. We describe the sequential andthe parallel h; Gi-machine, and our implementation ofthem. We provide...