A negative result on depth-first net unfoldings

A successful way of palliating the state-explosion problem when model-checking concurrent systems is to apply partial-order techniques. These techniques allow to verify properties without exhaustively exploring all the reachable states of the system. Net unfoldings are a partial-order technique based on the theory of true concurrency. Introduced by McMillan in [12,13], it has since then been further analyzed and improved [6–8,15], extended to full LTL model checking [3–5], to symmetrical systems [2] and to nets with read arcs [16], and applied, e.g., to conformance checking [14], analysis of asynchronous circuits [9,10] and graphgrammars [1]. The technique requires the system to be modelled as a collection of communicating automata, as a Petri net, or in any other formalism with a notion of concurrent components and specifying which components participate in each action. In this paper, we use the Petri net formalism.