19th International Workshop on Termination

August 24-25, 2023, University Center Obergurgl, Austria. (Google Map)

As part of Obergurgl Summer on Rewriting 2023 and co-located with IWC 2023.

Background

The Workshop on Termination (WST) traditionally brings together, in an informal setting, researchers interested in all aspects of termination, whether this interest be practical or theoretical, primary or derived. The workshop also provides a ground for cross-fertilization of ideas from the different communities interested in termination (e.g., working on computational mechanisms, programming languages, software engineering, constraint solving, etc.). The friendly atmosphere enables fruitful exchanges leading to joint research and subsequent publications.

The 19th International Workshop on Termination (WST 2023) continues the successful workshops held in St. Andrews (1993), La Bresse (1995), Ede (1997), Dagstuhl (1999), Utrecht (2001), Valencia (2003), Aachen (2004), Seattle (2006), Paris (2007), Leipzig (2009), Edinburgh (2010), Obergurgl (2012), Bertinoro (2013), Vienna (2014), Obergurgl (2016), Oxford (2018), virtually (2021), and Haifa (2022).

Workshop Topics

The 19th International Workshop on Termination welcomes contributions on all aspects of termination. In particular, papers investigating applications of termination (for example in complexity analysis, program analysis and transformation, theorem proving, program correctness, modeling computational systems, etc.) are very welcome.

Topics of interest include (but are not limited to):

• termination and complexity analysis in any domain (lambda calculus, declarative programming, rewriting, transition systems, probabilistic programs, etc.)
• abstraction methods in termination analysis
• certification of termination and complexity proofs
• challenging termination problems
• comparison and classification of termination methods
• implementation of termination and complexity methods
• non-termination analysis and loop detection
• normalization and infinitary normalization
• operational termination of logic-based systems
• ordinal notation and subrecursive hierarchies
• SAT, SMT, and constraint solving for (non-)termination analysis
• scalability and modularity of termination methods
• well-founded relations and well-quasi-orders

Termination Competition

Since 2003, the catalytic effect of WST to stimulate new research on termination has been enhanced by the celebration of the Termination_Competition and its continuously developing problem databases containing thousands of programs as challenges for termination analysis in different categories. In 2023, the Termination Competition will run shortly before WST. Tool/benchmark authors are invited to submit a short tool paper and give a presentation on the workshop.

Keynote Speaker

Benjamin Kaminski, Saarland U. Termination of Probabilistic Programs

Abstract Unlike for ordinary programs, termination of probabilistic programs is more nuanced: A probabilistic program can terminate with probability 1 while still needing infinitely many computation steps in expectation. We will explore the complexity landscape of probabilistic program termination and present proof rules for proving both almost-sure termination (i.e. termination with probability 1) as well as positive almost-sure termination (i.e. termination within finite expected time). Time permitting, we will furthermore dive into open problems on termination of weighted programs – a generalization of probabilistic programs where branches can be associated with more general weights from a semiring.

Program

Thursday 24 August

Session 1: Keynote & Probabilistic Termination (Chair: Akihisa Yamada)

14:00	Benjamin Kaminski: Termination of Probabilistic Programs (invited talk)
15:00	Jan-Christoph Kassing and Jürgen Giesl: Dependency Tuples for Almost-Sure Innermost Termination of Probabilistic Term Rewriting (paper)
15:30	coffee break

Session 2: Termination of Term Rewriting (Chair: Johannes Waldmann)

16:00	Fabian Mitterwallner, Aart Middeldorp and René Thiemann: Linear Termination over N is Undecidable (paper)
16:30	Teppei Saito and Nao Hirokawa: Generalizing Weighted Path Orders (paper)
17:00	René Thiemann and Elias Wenninger: A Verified Efficient Implementation of the Weighted Path Order (paper)
17:30	Nao Hirokawa and Aart Middeldorp: Hydra Battles and AC Termination, Revisited (paper)
18:00

Friday 25 August

Session 3: Termination beyond Term Rewriting (Chair: Carsten Fuhs)

9:00	Ayuka Matsumi, Naoki Nishida, Misaki Kojima and Donghoon Shin: On Singleton Self-Loop Removal for Termination of LCTRSs with Bit-Vector Arithmetic (paper)
9:30	Liye Guo and Cynthia Kop: Higher-Order LCTRSs and Their Termination (paper)
10:00	Jera Hensel and Jürgen Giesl: Automated Termination Proofs for C Programs with Lists (paper)
10:30	coffee break

Session 4: Non-Termination (Chair: René Thiemann)

11:00	Dieter Hofbauer and Johannes Waldmann: Old and New Benchmarks for Relative Termination of String Rewrite Systems (paper)
11:30	Florian Frohn and Jürgen Giesl: Proving Non-Termination by Acceleration Driven Clause Learning (paper)
12:00	Étienne Payet: Binary Non-Termination in Term Rewriting and Logic Programming (paper)
12:30	lunch

Session 5: Complexity Analysis and Probabilistic termCOMP (Chair: Benjamin Kaminski)

14:00	Nils Lommen, Eleanore Meyer and Jürgen Giesl: Automated Complexity Analysis of Integer Programs via Triangular Weakly Non-Linear Loops (paper)
14:30	Cynthia Kop and Deivid Vale: Complexity Analysis for Call-by-Value Higher-Order Rewriting (paper)
15:00	0th Probabilistic termCOMP
15:30	coffee break

Session 6: termCOMP 2023 and business meeting (Chair: Akihisa Yamada)

16:00	Nils Lommen, Eleanore Meyer and Jürgen Giesl: KoAT: An Automatic Complexity Analysis Tool for Integer Programs
16:15	Florian Frohn and Jürgen Giesl: Proving Non-Termination and Lower Runtime Bounds via ADCL with LoAT
16:30	Jürgen Giesl, Daniel Cloerkes, Stefan Dollase, Florian Frohn, Carsten Fuhs, Jera Hensel, Jan-Christoph Kassing, Nils Lommen and Eleanore Meyer: AProVE 2023
16:45	Fred Mesnard and Étienne Payet: NTI+cTI: a Logic Programming Termination Analyzer
17:00	Dieter Hofbauer: MultumNonMulta entering Term Rewriting
17:15	Akihisa Yamada: Results of the Termination Competition 2023
17:30	business meeting

Submission Guidelines

Submissions are short papers/extended abstracts which should not exceed 5 pages. There will be no formal reviewing. In particular, we welcome short versions of recently published articles and papers submitted elsewhere. The program committee checks relevance and provides additional feedback for each submission. The accepted papers will be made available electronically before the workshop.

Papers should be submitted electronically via the submission page.

Please use LaTeX and the LIPIcs style file to prepare your submission.

Important Dates

• title and abstract submission: June 1
• paper submission: June 8
• notification: June 15
• final version: July 27
• workshop: August 24-25

Program Committee

• Martin Avanzini, INRIA Sophia Antipolis
• Florian Frohn, RWTH Aachen
• Carsten Fuhs, Birkbeck, U. London
• Raúl Gutiérrez, U. Politécnica de Madrid
• Étienne Payet, U. La Réunion
• Albert Rubio, Complutense U. Madrid
• René Thiemann, U. Innsbruck
• Deivid Vale, Radboud U. Nijmegen
• Johannes Waldmann, HTWK Leipzig
• Akihisa Yamada, AIST Tokyo Waterfront (chair)