Models for name-passing processes: interleaving and causal

We study syntax-free models for name-passing processes. For interleaving semantics, we identify the indexing structure required of an early labelled transition system to support the usual /spl pi/-calculus operations, defining indexed labelled transition systems. For non-interleaving causal semantics, we define indexed labelled asynchronous transition systems, smoothly generalizing both our interleaving model and the standard asynchronous transition systems model for CCS-like calculi. In each case we relate a denotational semantics to an operational view for bisimulation and causal bisimulation respectively. This is a first step towards a uniform understanding of the semantics and operations of name-passing calculi.