In: Theoretical Computer Science, Vol. 64, No. 3, pages 221-269. May 1989.
Abstract: Concurrent transition systems (CTS's) are ordinary nondeterministic transition systems that have been equipped with additional concurrency information. This concurrency information is specified in terms of a binary residual operation on transitions, which describes how certain pairs of transitions ``commute''. The defining axioms for a CTS generate a rich algebraic theory, which is developed in detail.