Open bisimilarity is an equivalence relation for the π-calculus that is also congruence, making it suitable to use in compositional reasoning for mobile processes and communication protocols. The original definition of open bisimilarity, due to Sangiorgi, does not account for the mismatch operator, that is crucial in modelling real-world protocols. When mismatch is present, the congruence property no longer holds for open bisimilarity. In a LICS 2018 paper, Horne et al. proposed an extension of open bisimilarity, using a history-indexed class of relations, to address this problem. That definition, however, turns out to be non-compositional as we shall demonstrate in this paper. This paper presents a new definition of open bisimilarity in the π-calculus that incorporates mismatch. This is achieved by augmenting the transition semantics of the π-calculus with an explicit assumption about name distinctions, and by requiring that open bisimulation to be closed under an arbitary extension of the name distinctions assumption. We then prove that the resulting open bisimilarity is both an equivalence relation and a congruence.
@InProceedings{liu_et_al:LIPIcs.CONCUR.2025.30, author = {Liu, Tiange and Tiu, Alwen and Horne, Ross}, title = {{Open Bisimilarity for the \pi-Calculus with Mismatch}}, booktitle = {36th International Conference on Concurrency Theory (CONCUR 2025)}, pages = {30:1--30:20}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-389-8}, ISSN = {1868-8969}, year = {2025}, volume = {348}, editor = {Bouyer, Patricia and van de Pol, Jaco}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.30}, URN = {urn:nbn:de:0030-drops-239805}, doi = {10.4230/LIPIcs.CONCUR.2025.30}, annote = {Keywords: mismatch, open bisimilarity, pi calculus} }
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