Abstract. The product of safe Petri nets is a well known operation: it generalizes to concurrent systems the usual synchronous product of automata. In this paper, we consider a more general way of combining nets, called a pullback. The pullback operation generalizes the product to nets which interact both by synchronized transitions and/or by a shared sub-net (i.e. shared places and transitions). To obtain all pullbacks, we actually show that all equalizers can be defined in the category of safe

For synthesising efficient asynchronous circuits one has to deal with the state space explosion problem. In this paper, we present a combined approach to alleviate it, based on using Petri net unfoldings and decomposition. The experimental results show significant improvement in terms of runtime compared with other existing methods.

A combined framework for the resolution of encoding conflicts in STG unfoldings is presented, which extends previous work by incorporating concurrency reduction in addition to signal insertion. Furthermore, a novel validity condition is proposed to justify these transformations. 1

University of Newcastle upon Tyne,

The article discusses causal models, such as Petri nets and event structures, how they have been rediscovered in a wide variety of recent applications, and why they are fundamental to computer science. A discussion of their present limitations leads to their extension with symmetry. The consequences, actual and potential, are discussed.

Synthesis of asynchronous circuits from Signal Transition Graphs (STGs) involves resolution of state encoding conflicts by means of refining the STG specification. In this paper, a fully automatic technique for resolving such conflicts by means of insertion of new signals and concurrency reduction is proposed. It is based on conflict cores, i.e., sets of transitions causing encoding conflicts, which are represented at the level of finite and complete unfolding prefixes, and a SAT solver is used to find where in the STG the transitions of new signals should be inserted and to check the validity of concurrency reductions. The experimental results show significant improvements over the state space based approach in terms of runtime and memory consumption, as well as some improvements in the quality of the resulting circuits.

A combined framework for the resolution of encoding conflicts in STG unfoldings is presented, which extends previous work by incorporating concurrency reduction in addition to signal insertion. Furthermore, a novel validity condition is proposed to justify these transformations.

A technique for logic decomposition of asynchronous circuits which works on STG unfolding prefixes rather than state graphs is proposed. It retains all the advantages of the state space based approach, such as the possibility of multiway acknowledgement, latch utilisation and highly optimised circuits. Moreover, it significantly alleviates the state space explosion, and thus has superior memory consumption and runtime.