The aim of the LOPSTR series is to stimulate and promote international research and collaboration on logic-based program development. LOPSTR is open to contributions in logic-based program development in any language paradigm. LOPSTR has a reputation for being a lively, friendly forum for presenting and discussing work in progress. Formal proceedings are produced only after the symposium so that authors can incorporate this feedback in the published papers.

The 31st International Symposium on Logic-based Program Synthesis and Transformation (LOPSTR 2021) will be held as a hybrid (blended) meeting, both in-person (at the Teachers' House in Tallinn, Estonia) and virtual. Previous symposia were held in Bologna (as a virtual meeting), Porto, Frankfurt am Main, Namur, Edinburgh, Siena, Canterbury, Madrid, Leuven, Odense, Hagenberg, Coimbra, Valencia, Lyngby, Venice, London, Verona, Uppsala, Madrid, Paphos, London, Venice, Manchester, Leuven, Stockholm, Arnhem, Pisa, Louvain-la-Neuve and Manchester (you might have a look at the contents of past LOPSTR symposia at DBLP).

LOPSTR 2021 will be co-located with PPDP 2021. Information about venue and travel is available on the joint PPDP/LOPSTR conference website.

Topics of interest cover all aspects of logic-based program development, all stages of the software life cycle, and issues of both programming-in-the-small and programming-in-the-large, including, but not limited to:

Both full papers and extended abstracts describing foundations and applications in these areas are welcome. Survey papers that present some aspects of the above topics from a new perspective and papers that describe experience with industrial applications are also welcome.

Papers must describe original work, be written and presented in English, and must not substantially overlap with papers that have been published or that are simultaneously submitted to a journal, conference, or workshop with refereed proceedings. Work that already appeared in unpublished or informally published workshop proceedings may be submitted (please contact the PC chairs in case of questions).

Program & Schedule

The schedule is given in EEST (Eastern European Summer Time), local to Tallinn.

Tuesday 7 September
11:20 - 11:30	Opening
11:30 - 13:00	Session I - Chair: German Vidal Joao Barbosa, Mário Florido and Vítor Santos Costa Data Type Inference for Logic Programming Maciej Buszka and Dariusz Biernacki Automating the Functional Correspondence between Higher-Order Evaluators and Abstract Machines
13:00 - 14:30	Lunch Break
14:30 - 16:00	Session II - Chair: Michael Hanus Włodzimierz Drabent S-semantics - an example Alexander Vandenbroucke and Tom Schrijvers Disjunctive Delimited Control
16:00 - 16:30	Coffee Break
16:30 - 18:00	Session III - Chair: Maja Kirkeby Marco Mantovani and Alberto Momigliano Towards Substructural Property-Based Testing Andrei Nemytykh On Specialization of a Program Model of Naive Pattern Matching in Strings
18:00 - 19:00	Reception
19:00 - 20:00	INVITED TALK (PPDP+LOPSTR) - Chair: Silvia Ghilezan Stephen Wolfram, Wolfram Research Title: The Computational Structure of the Universe and of Programs Abstract: I'll talk about my emerging new foundational understanding of computation based on three large-scale projects: (1) Our recent Physics Project, which provides a fundamentally computational model for the low-level operation of our universe, (2) My long-time investigation of the typical behavior of simple programs (such as cellular automata, combinators, etc.) in the computational universe and (3) The long-time development of the Wolfram Language as a computational language to describe the world. I'll describe my emerging concept of the multicomputational paradigm---and some of its implications for science, distributed computing, language design and the foundations of computation and mathematics.

Wednesday 8 September
10:00 - 11:00	INVITED TALK (PPDP+LOPSTR) - Chair: Bishoksan Kafle Harald Søndergaard, University of Melbourne Title: String abstract domains and their combination Abstract: Strings are challenging for static analysis. The perennial problem in static analysis, of finding a good balance between precision and efficiency, is particularly unwieldy for string analysis. For static reasoning about strings, many string facets are of potential relevance, such as length, shape, and the characters used. Hence abstract interpretations of string manipulating programs tend to either employ an expressive but expensive abstract domain, or else combine a number of cheaper domains, each designed to capture a specific aspect of strings. In the presentation I will discuss frameworks for abstract domain combination and survey recent developments in string static analysis.
11:00 - 11:30	Coffee Break
11:30 - 13:00	Session IV - Chair: Vitor Santos Costa Geoff Hamilton The Next 700 Program Transformers Manolis Pitsikalis, Alexei Lisitsa and Shan Luo Representation and Processing of Instantaneous and Durative Temporal Phenomena
13:00 - 15:00	Lunch Break
15:00 - 16:00	TUTORIAL - Chair: Alberto Pettorossi Włodzimierz Drabent, IPI PAN, Poland & Linköping University, Sweden Title: It is declarative. On practical declarative programming in Prolog Abstract: It often seems that, in the practical programming in Prolog, not much remains from the ideas of logic programming, or declarative programming. We argue that practical programming in Prolog can actually be made declarative, to an extent larger than usually understood. We show how to reason about correctness (and completeness) of programs, and discuss the role of approximate specifications. We show a systematic way of constructing correct and complete programs out of specifications. We recall the forgotten idea of declarative diagnosis (algorithmic debugging), and show how it could be made practically viable.
16:00 - 16:30	Coffee Break
16:30 - 18:00	Session V - Chair: Alberto Pettorossi Juan José González-Abril and German Vidal A Program Instrumentation for Prefix-Based Tracing in Message-Passing Concurrency Marco Comini, Maria-Del-Mar Gallardo and Alicia Villanueva A denotational semantics for PROMELA addressing arbitrary jumps
18:00 - 18:30	Closing

Invited speakers

Harald Søndergaard, University of Melbourne (joint PPDP-LOPSTR invited speaker)

Title: String abstract domains and their combination

Abtract: Strings are challenging for static analysis. The perennial problem in static analysis, of finding a good balance between precision and efficiency, is particularly unwieldy for string analysis. For static reasoning about strings, many string facets are of potential relevance, such as length, shape, and the characters used. Hence abstract interpretations of string manipulating programs tend to either employ an expressive but expensive abstract domain, or else combine a number of cheaper domains, each designed to capture a specific aspect of strings. In the presentation I will discuss frameworks for abstract domain combination and survey recent developments in string static analysis.

Stephen Wolfram, Wolfram Research (joint PPDP-LOPSTR invited speaker)

Title: The Computational Structure of the Universe and of Programs

Abtract: I'll talk about my emerging new foundational understanding of computation based on three large-scale projects: (1) Our recent Physics Project, which provides a fundamentally computational model for the low-level operation of our universe, (2) My long-time investigation of the typical behavior of simple programs (such as cellular automata, combinators, etc.) in the computational universe and (3) The long-time development of the Wolfram Language as a computational language to describe the world. I'll describe my emerging concept of the multicomputational paradigm---and some of its implications for science, distributed computing, language design and the foundations of computation and mathematics.

Accepted papers

• Joao Barbosa, Mário Florido and Vítor Santos Costa. Data Type Inference for Logic Programming
• Maciej Buszka and Dariusz Biernacki. Automating the Functional Correspondence between Higher-Order Evaluators and Abstract Machines
• Włodzimierz Drabent. S-semantics - an example
• Alexander Vandenbroucke and Tom Schrijvers. Disjunctive Delimited Control
• Marco Mantovani and Alberto Momigliano. Towards Substructural Property-Based Testing
• Andrei Nemytykh. On Specialization of a Program Model of Naive Pattern Matching in Strings (Extended Abstract)
• Geoff Hamilton. The Next 700 Program Transformers
• Manolis Pitsikalis, Alexei Lisitsa and Shan Luo Representation and Processing of Instantaneous and Durative Temporal Phenomena
• Juan José González-Abril and German Vidal. A Program Instrumentation for Prefix-Based Tracing in Message-Passing Concurrency
• Marco Comini, Maria-Del-Mar Gallardo and Alicia Villanueva. A denotational semantics for PROMELA addressing arbitrary jumps

• Abstract submission (optional)

  01 May 2021

  Paper submission

  15 May 2021

  25 June 2021

  (see Submission Guidelines)

• Notification

  01 July 2021

  16 July 2021

• Camera-ready

  for pre-proceedings

  27 August 2021

  pre-proceedings will be archived on arXiv.org

• Conference

  07-08 September 2021

• Revised paper submission

  01 November 2021

• Notification

  01 December 2021

• Final version

  for post-proceedings

  16 January 2022

The formal post-conference proceedings will be published by Springer in the Lecture Notes in Computer Science series as in previous years (the complete list of previous LOPSTR proceedings is available here). Full papers can be directly accepted for publication in the formal proceedings, or accepted only for presentation at the symposium and inclusion in informal proceedings. After the symposium, all authors of extended abstracts and full papers accepted only for presentation will be invited to revise and/or extend their submissions. Then, after another round of reviewing, these revised papers may also be published in the formal proceedings. Authors should consult Springer's authors' instructions and use their proceedings templates, either for LaTeX (available also in Overleaf) or for Word, for the preparation of their papers. Springer encourages authors to include their ORCIDs in their papers. In addition, the corresponding author of each paper, acting on behalf of all of the authors of that paper, must complete and sign a Consent-to-Publish form. The corresponding author signing the copyright form should match the corresponding author marked on the paper. Once the files have been sent to Springer, changes relating to the authorship of the papers cannot be made.

Up to two outstanding papers will be invited to submit a rapid publication in Theory and Practice of Logic Programming.

The informal pre-proceedings are available online at arXiv:2107.10160.

Thanks to Springer's sponsorship, a best paper award, which will include a 1000 EUR prize, will be given at LOPSTR 2021. The program committee will select the winning paper based on relevance, originality and technical quality but may also take authorship into account (e.g. a student paper).