Category Archives: Isabelle

(Self)Hosting of Mercurial Repositories

The Mercurial community has relied a bit too long on Bitbucket (by Atlassian) to provide “free” hosting for it. The ultimate purpose of such big corporations is to maximize profits and return of investments, while the needs of customers are of little concern, and marketing fills this semantic gap. Who did not know this triviality in advance, and merely ignored it on the spot when creating repositories on Bitbucket?

So the discontinuation of Mercurial by Bitbucket will happen in two stages, on 01-Feb-2020 and 01-Jun-2020. Independently of such market-driven policies, Mercurial developers are quite alive and active to develop alternatives. In the past few months, two emerging projects for (self)hosting of Mercurial repositories have gained some attention:

  1. Sourcehut as a newcomer for Git and Mercurial hosting
  2. Heptapod as a version of Gitlab for Mercurial (eventually both for Git and Mercurial). See also the blog for ongoing activity.

Development of these projects is very active, but they are not yet ready for production use.

In contrast, Phabricator is a pretty stable and scalable hosting platform right now; it supports Git, Mercurial, Subversion. In fact, Phabricator is a sophisticated platform for software project management, and repository hosting is only a secondary function of it. See also the related post on Isabelle/Phabrictor tooling, with Isabelle development as a notable example.

Update 21-Mar-2020: link to Heptapod blog.

Isabelle/Phabricator server setup

Recent Isabelle repository versions (or release candidates for Isabelle2020) include support for Phabricator; a current release snapshot is also available. The following introduction to Isabelle/Phabricator is from the system manual (chapter 6).

Phabricator is an open-source product to support the development process of complex software projects (open or closed ones). The official slogan is:

Discuss. Plan. Code. Review. Test.
Every application your project needs, all in one tool.

Ongoing changes and discussions about changes are maintained uniformly within a MySQL database. There are standard connections to major version control systems: Subversion, Mercurial, Git. So Phabricator offers a counter-model to trends of monoculture and centralized version control, especially due to Microsoft’s Github and Atlassian’s Bitbucket.

The small company behind Phabricator provides paid plans for support and hosting of servers, but it is easy to do independent self-hosting on a standard LAMP server (Linux, Apache, MySQL, PHP). This merely requires a virtual machine on the Net, which can be rented cheaply from local hosting providers — there is no need to follow big cloud corporations. So it is feasible to remain the master of your virtual home, following the slogan “own all your data”. In many respects, Phabricator is similar to the well-known Nextcloud product, concerning both the technology and sociology.

The following Phabricator instances may serve as examples:

Initial Phabricator configuration requires many details to be done right. Isabelle provides some command-line tools to help with the setup, and afterwards Isabelle support is optional: it is possible to run and maintain the server, without requiring the somewhat bulky Isabelle distribution again.

Assuming an existing Phabricator installation, the command-line tool isabelle hg_setup helps to create new repositories or to migrate old ones. In particular, this avoids the lengthy sequence of clicks in Phabricator to make a new private repository with hosting on the server. (Phabricator is a software project management platform, where initial repository setup happens rarely in practice.)

Update 20-Jan-2020: follow Isabelle/597059a44d6f.

Update 21-Mar-2020: link to release candidates of Isabelle2020.

Isabelle as “the world’s most complicated video game”

Martin Kleppmann from the University of Cambridge has given very nice introductory lectures about formal verification with Isabelle: the title is Correctness proofs of distributed systems with Isabelle, see these slides. Further information and video recordings are available from here:

The lecture motivates the use of Isabelle by the very fitting characterization by Dominic Mulligan: Isabelle is the world’s most complicated video game.

Later in the talk there is a hands-on demo of the Isabelle Prover IDE, using the standard Isabelle/jEdit front-end: this is not a classic “REPL”, but a semantic document editor with immediate feedback by the prover.

Update (19-Dec-2019): An extended version of both talks is now available.

Talk on Export of formal theory content

On 22-Nov-2019 I have delivered the following talk at TUM (Garching bei München):

Export of formal theory content in Isabelle/Scala
This is an overview of the state of affairs of systematic export of formal theory content. The general motivation is to provide semantically enriched views on the Isabelle/AFP library, without requiring a running Isabelle process. A typical application could be search over a database of digested theories, e.g. for an AFP web service.
Slides with sources, which include practically relevant links and examples.

MMT as component for Isabelle2019

MMT is a language, system and library (in Scala) to represent a broad range of languages in the OMDoc format: this supports formal, informal, semi-formal content. The MMT repository includes
general APIs to operate on OMDoc theories, together with various tools and applications. There are several MMT sub-projects to connect to other systems. This includes Isabelle/MMT, which appeared as preliminary version already in Nov-2018.

The release of Isabelle2019 (June 2019) is an opportunity to distribute MMT version 17.0.0 (May 2019) as Isabelle application. An alternative is to incorporate the underlying Isabelle component manually into Isabelle2019 in $ISABELLE_HOME_USER/etc/settings like this: init_component ".../mmt-20190611" — where the three dots refer to the directory where the component tar.gz has been unpacked.

In either case, the mmt.jar of the MMT distribution is included in the Isabelle/Scala package name space. The component provides Isabelle command-line tools as follows:

  • isabelle mmt_build to (re)build the MMT project inside the Isabelle system environment (only required after change of the Scala sources)
  • isabelle mmt_import to import the content of a headless Isabelle/PIDE session into MMT (OMDoc and RDF/XML triples)
  • isabelle mmt_server to present imported content using the built-in HTTP server of MMT
  • isabelle mmt to run the interactive MMT shell inside the Isabelle system environment, e.g. for experimentation within the Isabelle + MMT package namespace, using the scala sub-shell.

The main functionality is provided by isabelle mmt_import: that is a medium-sized Scala module (57KB) within the MMT code-base (file src/mmt-isabelle/src/info/kwarc/mmt/isabelle/Importer.scala). It refers to general export facilities of Isabelle/Scala, which are part of the Isabelle2019 distribution (file src/Pure/Thy/export_theory.scala). The latter may be studied independently of MMT in the implementation of the isabelle dump tool (file src/Pure/Tools/dump.scala); see also the Isabelle System Manual, section 2.6.

The following papers provide further explanations on Isabelle/MMT:

Isabelle/Naproche for Automatic Proof-Checking of Ordinary Mathematical Texts

Naproche-SAD is a recent tool by Frerix and Koepke, based on the original System for Automated Deduction (SAD) by Paskevich and others. It processes the Formal Theory Language (ForTheL), which is designed to look like mathematical text, but it is restricted to a small subset of natural language.

The tool is implemented in Haskell as a plain function from input text to output messages. A file is like a chapter of mathematical text, with a nested tree-structure of elements and sub-elements (for signatures, axiomatizations, statements, proofs). Output messages inform about the translation of mathematical text to problems of first-order logic, and indicate success or failure of external proof checking; the latter is delegated to the E Prover by Stephan Schulz and can take several seconds for each proof obligation.

To integrate Naproche-SAD into PIDE, Frerix and Wenzel have reworked the Haskell program over 2 months in 2018, to turn the command-line tool into a service for reactive checking of ForTheL texts. Isabelle integration was done via the new Isabelle/Haskell library and some glue code in Isabelle/Scala to register ForTheL as auxiliary file-format (extension .ftl).

[Isabelle/Naproche screenshot]

The resulting Isabelle/Naproche application is available as multi-platform download. A running instance is shown in the screenshot: users can directly open ForTheL files (e.g. from Documentation / Examples) and wait briefly to see output messages attached to the text in the usual IDE manner. Further edits produce a new version of the text, which is sent in total to Naproche-SAD again. The back-end is sufficiently smart to avoid redundant checking of unchanged sub-elements: it keeps a global state with results of old versions: this is easy to implement as the program keeps running until shutdown of Isabelle/PIDE.

(Cited from section 1.2 of the paper Interaction with Formal Mathematical Documents in Isabelle/PIDE.)

Isabelle presentations at LSV Paris/Cachan

During the two weeks of 17..28-Jun-2019, I will be visiting Deducteam at LSV, Paris/Cachan. There will be two presentations about Isabelle technology for formal documents and libraries:

  1. Interaction with Formal Mathematical Documents in Isabelle/PIDE (with slides) – Tuesday 18-Jun-2019, 11:00, Pavillon du Jardin, ENS Cachan.
  2. Isabelle technology for the Archive of Formal Proofs (with slides) – Thursday 20-Jun-2019, 14:00, LSV library.

See also the official announcement of Deducteam.

Note: These talks will be repeated at the Conference on Intelligent Computer Mathematics (CICM 2019), Prague (CZ), 08..12-Jul-2019.