maintained that a basic lesson can be learned from Prolog and the Prolog-like concurrent systems: a universal model of concurrent computation is limited by having any mandatory overhead in the basic communication mechanisms. This is an argument against including pattern-directed invocation using unification and extraction of messages from data structure streams as fundamental primitives. But compare Shapiro's survey of Prolog-like concurrent programming languages for arguments for inclusion. Indeterminacy in other models of computation Arbitration is the basis of the indeterminacy in the Actor model of concurrent computation (see History of the Actor model and Actor model theory). It may also play a role in other models of concurrent systems such as process calculi. See also Quantum computing Randomized algorithm Non-deterministic Turing machine References Carl Hewitt What is computation? Actor Model versus Turing's Model in A Computable Universe: Understanding Computation & Exploring Nature as Computation. Dedicated to the memory of Alan M. Turing on the 100th anniversary of his birth. Edited by Hector Zenil. World Scientific Publishing Company. 2012 Carl Hewitt. PLANNER: A Language for Proving Theorems in Robots IJCAI 1969. Carl Hewitt. Procedural Embedding of Knowledge In Planner IJCAI 1971. Carl Hewitt, Peter Bishop and Richard Steiger. A Universal Modular Actor Formalism for Artificial Intelligence IJCAI 1973. Robert Kowalski Predicate Logic as Programming Language Memo 70, Department of Artificial Intelligence, Edinburgh University. 1973. Pat Hayes. Computation and Deduction Mathematical Foundations of Computer Science: Proceedings of Symposium and Summer School, Štrbské Pleso, High Tatras, Czechoslovakia, September 3–8, 1973. Carl Hewitt and Henry Baker Laws for Communicating Parallel Processes IFIP-77, August 1977. Carl Hewitt. Viewing Control Structures as Patterns of Passing Messages Journal of Artificial Intelligence. June 1977. Henry Baker. Actor Systems for Real-Time Computation MIT EECS Doctoral Dissertation. January 1978. Bill Kornfeld and Carl Hewitt. The Scientific Community Metaphor IEEE Transactions on Systems, Man and Cybernetics. January 1981. Will Clinger. Foundations of Actor Semantics MIT Mathematics Doctoral Dissertation. June 1981. Carl Hewitt. The Challenge of Open Systems Byte Magazine. April 1985. Reprinted in The foundation of artificial intelligence–a sourcebook Cambridge University Press. 1990. Gul Agha. Actors: A Model of Concurrent Computation in Distributed Systems Doctoral Dissertation. MIT Press. 1986. Robert Kowalski. The limitation of logic Proceedings of the 1986 ACM 14th Annual Conference on Computer science. Ehud Shapiro (Editor). Concurrent Prolog MIT Press. 1987. Robert Kowalski. The Early Years of Logic Programming Communications of the ACM. January 1988. Ehud Shapiro. The