Event structures are a basic model of computation introduced by Nielsen, Plotkin, and Winskel [1].

To introduce a convenient parallel composition operation, Boudol and Castellani [2] worked with a model called flow event structures. By disallowing arbitrary confusion (meaning a certain technical combination of causality, concurrency, and conflict), Castellani and Zhang [3] obtained a well-behaved parallel composition.

The authors of this paper wish to allow an event refinement operation as well, for which they introduce a new condition of well-behavedness in the parallel composition operation. This paper will be of interest to researchers in process calculi and the semantics of parallelism.