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What is Twelf?

Twelf is a language used to specify, implement, and prove properties of deductive systems such as programming languages and logics. Large research projects using Twelf include the TALT typed assembly language, a foundational proof-carrying-code system, and a type safety proof for Standard ML.

Visitors without a technical background are encouraged to read the general description of Twelf.

Download and Learn Twelf
Download Twelf or try it online.

Learn Twelf:

See the documentation page for more resources.

What's new?

June 10, 2013
October 26, 2012
September 2, 2011
  • We've finally moved from to! All old links will continue to work through at least August 2013 (and they should actually continue to work indefinitely).
March 19, 2011
  • After many years of new features being added only to the subversion branch, Twelf now has a new official point release! Twelf 1.7.1 contains many fixes and new features that are documented on this site, and using any version of Twelf prior to 1.7 is highly discouraged. The "development" version of Twelf in the subversion repository remains quite stable and is also recommended. Go to the download page to get Twelf.
September 1, 2010
  • The Twelf Wiki has undergone an upgrade, and in the process code underlying the syntax-highlighing TwelfTag system has been substantially rewritten and simplified. However, this meant several deprecated-but-still-used options to the <twelf> tags now don't work and print error messages. Leave a note on Rob's talk page if you see any weird error messages around Twelf code.
February 22, 2009
  • Rob has a case study on lax logic that uses the admissibility of cut and identity show a sound and complete correspondence between two sequent calculus presentations of lax logic.
October 1, 2008
  • Carsten says: As a result of the work of some overly active system administrators at the ITU, the twelf mailing list was accidentally erased a few weeks ago. Since then I have tried to reconstruct the subscriber list with more or less success, but there are still some that I have missed. Therefore, if you haven't received any mail from the list lately, but you expect to be on it, please resubscribe under [].

To read about older updates, see the What's new? page.

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