eprintid: 10130031 rev_number: 25 eprint_status: archive userid: 608 dir: disk0/10/13/00/31 datestamp: 2021-07-21 11:55:39 lastmod: 2022-05-03 13:51:13 status_changed: 2022-05-03 13:39:40 type: proceedings_section metadata_visibility: show creators_name: Schmid, T creators_name: Rot, J creators_name: Silva, A title: On Star Expressions and Completeness Theorems ispublished: pub divisions: UCL divisions: B04 divisions: C05 divisions: F48 keywords: Regular expressions, bisimulation, program semantics, coalgebra. note: © T. Schmid, J. Rot, & A. Silva This work is licensed under the Creative Commons Attribution License. abstract: An open problem posed by Milner asks for a proof that a certain axiomatisation, which Milner showed is sound with respect to bisimilarity for regular expressions, is also complete. One of the main difficulties of the problem is the lack of a full Kleene theorem, since there are automata that can not be specified, up to bisimilarity, by an expression. Grabmayer and Fokkink (2020) characterise those automata that can be expressed by regular expressions without the constant 1, and use this characterisation to give a positive answer to Milner's question for this subset of expressions. In this paper, we analyse Grabmayer and Fokkink's proof of completeness from the perspective of universal coalgebra, and thereby give an abstract account of their proof method. We then compare this proof method to another approach to completeness proofs from coalgebraic language theory. This culminates in two abstract proof methods for completeness, what we call the local and global approaches, and a description of when one method can be used in place of the other. date: 2021-12 official_url: http://dx.doi.org/10.4204/EPTCS.351.15 oa_status: green full_text_type: other language: eng primo: open primo_central: open_green verified: verified_manual elements_id: 1871901 doi: 10.4204/EPTCS.351.15 lyricists_name: Silva, Alexandra lyricists_id: ASILV10 actors_name: Silva, Alexandra actors_id: ASILV10 actors_role: owner full_text_status: public series: EPTCS publication: arXiv.org volume: 351 pagerange: 242-259 event_title: MFPS 2021: 37th Conference on Mathematical Foundations of Programming Semantics book_title: Proceedings: 37th Conference on Mathematical Foundations of Programming Semantics citation: Schmid, T; Rot, J; Silva, A; (2021) On Star Expressions and Completeness Theorems. In: Proceedings: 37th Conference on Mathematical Foundations of Programming Semantics. (pp. pp. 242-259). Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/10130031/7/Silva_2106.08074v2.pdf