We consider a model for representing infinite-state and parameterized systems, in which states are represented as strings over a finite alphabet. Actions are transformations on strings, in which the change can be characterized by an arbitrary finite-state transducer. This program model is able to represent programs operating on a variety of data structures, such as queues, stacks, integers, and systems with a parameterized linear topology. The main contribution of this paper is an effective derivation of a general and powerful transitive closure operation for this model. The transitive closure of an action represents the effect of executing the action an arbitrary number of times. For example, the transitive closure of an action which transmits a single message to a buffer will be an action which sends an arbitrarily long sequence of messages to the buffer. Using this transitive closure operation, we show how to model and automatically verify safety properties for several types of infinite-state and parameterized systems.
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