Hierarchies and Characterizations of Stateless Multicounter Machines

We investigate the computing power of stateless multi- counter machines with reversal-bounded counters. Such a machine can be deterministic, nondeterministic, realtime (the input head moves right at every step), or non-realtime. The deterministic realtime stateless multicounter machines has been studied elsewhere [1]. Here we investigate non-realtime machines in both deterministic and nondeterministic cases with respect to the number of counters and reversals. We also consider closure properties and relate the models to stateless multihead automata and show that the bounded languages accepted correspond exactly to semilinear sets.