Functional Units for Natural Numbers
Interaction with services provided by an execution environment forms part of the behaviors exhibited by instruction sequences under execution. Mechanisms related to the kind of interaction in question have been proposed in the setting of thread algebra. Like thread, service is an abstract behavioral concept. The concept of a functional unit is similar to the concept of a service, but more concrete. A state space is inherent in the concept of a functional unit, whereas it is not inherent in the concept of a service. In this paper, the authors establish the existence of a universal computable functional unit for natural numbers and related results.