Petri nets are a well-known model of concurrency and provide an ideal setting for the study of fundamental aspects in concurrent systems. Despite their simplicity, they still lack a satisfactory causally reversible semantics. We develop such semantics for Place/Transitions Petri nets (P/T nets) based on two observations. Firstly, a net that explicitly expresses causality and conflict among events, for example an occurrence net, can be straightforwardly reversed by adding a reverse transition for each of its forward transitions. Secondly, given a P/T net the standard unfolding construction associates with it an occurrence net that preserves all of its computation. Consequently, the reversible semantics of a P/T net can be obtained as the reversible semantics of its unfolding. We show that such reversible behaviour can be expressed as a finite net whose tokens are coloured by causal histories. Colours in our encoding resemble the causal memories that are typical in reversible process calculi.

@article{MelgrattiMU20,
  title = {Reversing Place Transition Nets},
  author = {Hernán Melgratti and Claudio Antares Mezzina and Irek Ulidowski},
  journal = {Logical Methods in Computer Science},
  volume = {Volume 16, Issue 4},
  year = {2020},
  doi = {10.23638/lmcs-16(4:5)2020}
}