-------------------------------------------------------------------------------- IFIP Working Group 1.6 on Term Rewriting Report of the annual meeting: 31 July 2022 (Haifa, Israel, hybrid) Chair: Cynthia Kop Co-Chair/Secretary: Carsten Fuhs -------------------------------------------------------------------------------- PARTICIPANTS Aart Middeldorp Akihisa Yamada (online) Carsten Fuhs Cynthia Kop Dan Dougherty (online) Delia Kesner Femke van Raamsdonk Jörg Endrullis Jürgen Giesl Luigi Liquori (online) Luke Ong (online) Nachum Dershowitz Naoki Nishida (invited) Sandra Alves (invited) Sarah Winkler Silvia Ghilezan (online) Takihito Aoto (online) Vincent van Oostrom -------------------------------------------------------------------------------- AGENDA (1) Presentation Naoki Nishida (2) RLooP (the Rewriting List of open Problems) (3) Presentation Sandra Alves (4) The International School on Rewriting (5) Business Meeting (memberships, auxiliary topics) -------------------------------------------------------------------------------- (1) 09:00 Naoki Nishida Title: Inversion and Determinization in Term Rewriting Abstract: As a transformational approach, inversion is formulated in several settings, and the basic ideas are naive and similar. To generate a better form, e.g., non-overlapping systems if possible, determinization is used as a post-process of inversion for injective functions, and is the most challenging part in developing an inversion framework. In this talk, I introduce a framework of inversion and determinization in term rewriting. First, I explain a direct inversion of deterministic CTRSs, and a direct MSV-based determinization. Next, I explain the framework proposed by Gluck and Kawabe, which uses context-free grammars as intermediate representations of CTRSs. Finally, I explain a framework based on context-free expressions. (2) 10:00 Jörg Endrullis RLooP (the Rewriting List of open Problems) Jörg Endrullis reported on progress in setting up a new platform for the RTA List of open Problems (LooP) that was hosted by Nachum Dershowitz: The LooP consists of 107 problems, 35 of which solved, and has not received submissions since 2012. The new platform should serve for exchange of ideas, research questions, etc., and not only for posting difficult problems. To this end, a tagging system is planned, as well as the possibility to rate questions as interesting or difficult. Selected questions could be promoted to the official LooP. A prototype system is being implemented in Scala under GPL v3. Decisions to be made would include (i) a renaming from RTALooP to RLooP ("Rewriting List of open Problems"), (ii) whether to use an Open Data policy, and (iii) whether user ratings should be open or anonymous. Nachum Dershowitz pointed out that the selection committee for the list would be a bottleneck and that making the list more democratic setting could be beneficial. The suggestion was made that the platform itself be called "LooP", with "RLooP" as a specific instance. Cynthia Kop raised the question whether also non-members of the WG could participate in the selection committee. Aart Middeldorp asked whether old vague problems that were not overly well defined would be removed. The suggestion was made to tag these problems as "open ended". Nachum Dershowitz asked for volunteers for the selection committee. Luigi Liquori voiced his interest. (3) 11:00 Sandra Alves Title: Quantitative Weak Linearisation Abstract: Weak linearisation was defined years ago through a static characterisation of the intuitive notion of virtual redex, based on (legal) paths computed from the (syntactical) term tree. Weak-linear terms impose a linearity condition only on functions that are applied (consumed by reduction) and functions that are not applied (therefore persist in the term along any reduction) can be non-linear. This class of terms was shown to be strongly normalising with deciding typability in polynomial time. We revisit this notion through non-idempotent intersection types (also called quantitative types). By using an effective characterisation of minimal typings, based on the notion of tightness, we are able to distinguish between “consumed” and “persistent” term constructors, which allows us to define an expansion relation, between general lambda-terms and weak-linear lambda-terms, whilst preserving normal forms by reduction. (4) 12:00 Aart Middeldorp The International School on Rewriting (ISR) Aart Middeldorp first reported on ISR 2022 on behalf of the ISR Steering Committee and then proposed holding ISR 2024 in Obergurgl, organised by the University of Innsbruck: ISR 2022 takes place from 19 to 24 Sep in Tbilisi, Georgia. It has a basic track with an introduction to term rewriting and lambda calculus as well as an advanced track with 10 topics on rewriting theory and applications. The registration URL is https://viam.science.tsu.ge/clas2022/registration The deadline for early registration is on 14 August 2022, with a registration fee of EUR 200 for students and EUR 350 for non-students. Registration is encouraged! For ISR 2024, the suggestion would be to run the school at Obergurgl with two possible time slots, 21 - 28 July 2024 and 25 August 2024 - 1 September 2024. Pros and cons of the time slots were discussed. The point was made that a collision of the dates for ISR 2024 with FSCD 2024 should be avoided. An assessment of the bids for FSCD 2024 revealed that a clash was unlikely. Later the time slot was set to 25/08/24 - 01/09/24. ISR had already been organised successfully at the same location in 2008. The Steering Committee of ISR strongly supported the Obergurgl bid. (5) 16:00 IFIP WG 1.6 Business meeting Attendees included: Aart Middeldorp Carsten Fuhs Cynthia Kop Dan Dougherty (online) Delia Kesner Luigi Liquori (online) Luke Ong (online) Nachum Dershowitz Silvia Ghilezan (online) Takihito Aoto (online) Vincent van Oostrom The two invited speakers (Naoki Nishida, Sandra Alves) were voted unanimously to be invited to join IFIP WG 1.6 via an open vote. The proposal to hold ISR 2024 in Obergurgl was accepted unanimously. The date for ISR 2024 was discussed, with the decision ultimately left to the local organisers. RLooP was discussed as well, and its development was encouraged. Vincent van Oostrom suggested getting more young people into the WG. Carsten Fuhs suggested that some future meetings of the IFIP WG 1.6 could be co-located with ISR (as one of the main activities of the WG) to foster interaction. Luigi Liquori raised the point that Rewriting was currently not very well funded (in contrast to other areas of Computer Science) and that the WG could look into ways of raising funding for Rewriting-related activities. Further discussions were postponed to a planned full business meeting to be held virtually in Sep/Oct 2022.