Update bundled LIPIcs template from v2019 to v2021.1.3 #608

Description

The LIPIcs template bundled with rticles uses lipics-v2019.cls v2.2.1, imported from the LIPIcs distribution tagged v2019.2. Dagstuhl Publishing currently distributes LIPIcs v2021.1.3 as its supported author template. That distribution contains lipics-v2021.cls, whose internal class version is v3.1.3 (2023-05-12).

Authoritative sources for this update:

• Current publisher information: https://drops.dagstuhl.de/entities/series/LIPIcs#author
• Tagged upstream author kit: https://github.com/dagstuhl-publishing/styles/tree/v2021.1.3/LIPIcs/authors
• Tagged class file: https://github.com/dagstuhl-publishing/styles/blob/v2021.1.3/LIPIcs/authors/lipics-v2021.cls
• Publisher ZIP download: https://submission.dagstuhl.de/styles/download-tag/lipics/v2021.1.3/authors/zip

The rticles template should be reviewed and updated to follow this tagged publisher-provided class, its runtime assets, metadata interface, and author guidance. Mutable files from the upstream master branch should not be used as the copy source.

Relationship to the LaTeX 2026 failure

Related: #607

This update is intentionally tracked separately from #607. Updating to LIPIcs v2021.1.3 does not by itself fix the LaTeX 2026 / thmtools incompatibility: the unchanged official v2021.1.3 sample reproduces the same Command \c@lemma already defined error when thm-restate is enabled under the LaTeX 2026-06-01 kernel.

The mitigation added in #609 must therefore be preserved until a corrected upstream thmtools release is available. The skeleton should continue to make thm-restate opt-in.

Resource update

Compare the complete tagged v2021.1.3 author kit with the current rticles files and verify copied resources by hash.

Required runtime/resource changes currently identified:

• Replace lipics-v2019.cls with the exact tagged lipics-v2021.cls and update the document-class reference.
• Replace the publisher-provided cc-by.pdf, lipics-logo-bw.pdf, and orcid.pdf; the current assets differ from v2021.1.3.
• Update the bundled upstream CHANGELOG.md.
• Verify LICENSE.md and bibliography.bib against the tagged kit. They currently appear identical and should not be changed merely to produce a diff.
• Retain the appropriate LPPL license and upstream notices.

The upstream sample PDF and author-guidelines PDF are non-runtime reference files and do not need to be bundled. The rticles R Markdown skeleton remains the maintained example.

Pandoc template and v2021 interfaces

The rticles-owned resources/template.tex should be adapted rather than replaced by the upstream sample .tex. Preserve its metadata mapping, include hooks, bibliography and appendix placement, and compatibility blocks for supported Pandoc versions.

Review and expose the practical v2021 features through the R Markdown template where appropriate:

• subtitle
• pdfa
• compact author presentation, which is the v2021 default, with oldauthorstyle as an opt-out
• relatedversiondetails and supplementdetails
• conjecture and observation
• proofsubparagraph
• claimqedhere

Keep the existing simpler relatedversion and supplement metadata for backward compatibility. Preserve the bookdown theorem-preamble handling and the #607 compatibility hook.

The legacy Pandoc 3.1.7 citeproc block currently uses enumitem, which Dagstuhl discourages. Review whether it can be replaced without dropping rticles' supported older Pandoc behavior; do not remove compatibility code without equivalent coverage.

Citation and bibliography behavior

Dagstuhl's author guidance requires BibTeX with the fixed plainurl bibliography style and does not support author-year citations or use of the natbib LaTeX package.

This should not be implemented as policy enforcement by rticles. citation_package = "natbib" has been the lipics_article() default since the original contribution in #288, whose contributor reported using the template for submitted articles. In rmarkdown, this argument controls how Pandoc translates Markdown citation nodes; the custom LIPIcs Pandoc template does not contain Pandoc's usual block that loads the natbib LaTeX package. Conversely, citation_package = "default" selects citeproc and is not equivalent to Dagstuhl's required BibTeX workflow.

The update should therefore:

• Preserve the citation_package argument and user choice unless testing reveals an actual incompatibility.
• Test the current behavior before changing its default.
• Keep \bibliographystyle{plainurl} fixed in the generated LaTeX.
• Document and demonstrate the official BibTeX/plainurl route, including the citation syntax needed for it.
• Document how alternative citation_package values affect Pandoc processing, without warning about or rejecting deliberate user choices.

LaTeX engine

Dagstuhl recommends pdfLaTeX. rticles currently defaults to XeLaTeX solely because the skeleton uses a Unicode thin space in authorrunning.

Render the updated template with both pdfLaTeX and XeLaTeX, including its bibliography and representative v2021 features. If pdfLaTeX passes, replace the Unicode thin space with the LaTeX form \, and use pdfLaTeX by default. If it does not pass, retain XeLaTeX and document the tested reason and how users can request pdfLaTeX. Do not remove support for either engine unnecessarily.

Skeleton and documentation

Update the R Markdown skeleton and lipics_article() documentation to:

• Identify the v2021.1.3 distribution and lipics-v2021.cls v3.1.3 accurately.
• Use current publisher links and author instructions.
• Reflect the transition to CC BY 4.0 for published articles while retaining the distinct LPPL licensing of the source kit.
• Demonstrate the practical v2021 metadata and theorem/proof interfaces.
• Explain the official bibliography workflow and available citation-processing choices.
• Retain the editor-only volume macros, appendix placement, bookdown behavior, and opt-in theorem restatement guidance.

Tests and acceptance criteria

• The generated draft identifies and uses the tagged LIPIcs v2021.1.3 distribution's lipics-v2021.cls v3.1.3.
• Publisher-provided runtime resources match the tagged kit and retain the appropriate upstream license information.
• No unnecessary publisher-generated sample or documentation PDFs are added.
• The skeleton metadata and generated LaTeX follow current Dagstuhl author guidance while preserving compatible existing rticles metadata.
• Practical v2021 metadata and representative theorem/proof additions are covered without building an exhaustive option cross-product.
• Citation and bibliography behavior is tested and documented. The skeleton demonstrates Dagstuhl's BibTeX and plainurl workflow, while lipics_article() continues to permit users to select citation processing appropriate to their document.
• The updated template renders with both pdfLaTeX and XeLaTeX. The default is selected from those results and the documented Dagstuhl recommendation.
• Required Pandoc compatibility blocks remain covered by template-validation tests.
• The normal LIPIcs render and the legacy thm-restate render pass.
• Dedicated LIPIcs smoke coverage exercises both a pinned pre-2026 TeX kernel and the current 2026 kernel, without multiplying the complete Pandoc matrix.